Gastineau, Dennis A.

Abstract Background Immune editing is a major mechanism used by tumors to promote their survival. We have previously reported the presence of immunosuppressive monocytes (CD14+HLA-DR low/neg) in a number of cancers. Increased presence of these cells was associated with decreased treatment response and OS. Here we report an in vitro model to examine tumor monocyte cross talk and demonstrate that these monocytes may directly promote tumor cells’ resistance to chemotherapy. Method Monocytes from healthy donors were co-cultured with lymphoma cell lines (OCI-Ly1, OCI-Ly3, OCI-Ly7, OCI-Ly10, Su-DHL2, Su-DHL6, Jeko-1, Granta-519) with or without doxorubicin (DOX). Cultured cells were assessed for phenotype, viability, proliferation, and induced protein expression. Changes in vitro were confirmed in primary tissue by gene expression profile from 48 primary diffuse large B cell (DLBCL) lymphoma tumors. Results Monocytes converted CD14+HLA-DR+ to the CD14+HLA-DRlow/neg phenotype by co-culture with 5 of the 8 B cell lymphoma cell lines. The HLA-DR suppression was not due to the known regulatory effects of IL-10 nor was the effect seen in co-culture using B cells from healthy donors. Thus, the magnitude of DR loss is mediated by a yet undetermined mechanism. DOX incubation induced apoptosis in all of the cell lines. Co-culture with monocytes improved lymphoma cell survival in 3 of the 4 lymphoma cell lines. For example, untreated OCI-Ly3 had a 1.3±0.2 fold expansion that was reduced to 0.6±0.1 when treated with DOX (p<0.0001, n=13). However, when the cells were treated with DOX and co-cultured with monocytes the survival improved to 0.8±0.2 (p<0.0001, n=13). Having previously shown that CD14+HLA-DRlow/neg were capable of suppressing patient immunity, partially through arginase I, we determined if co-culture of monocytes with tumor cells increased arginase I expression in either monocytes or tumor cells. Not only did we see arginase I expression increases during co-culture(n=10, p<0.01), but surprisingly, the greatest increases were seen during co-culture and DOX treatment (n=10, p=0.01). To determine if our in vitro observations reflect human tumors, we used gene expression data obtained from 48 DLBCL tumors and found that increased CD14 gene expression was positively correlated with increased arginase I expression (n=48, p=0.02). Conclusions We have demonstrated that certain tumor cells induced phenotype changes in monocytes in an IL-10 independent and a tumor specific way. In those cells where tumors factors mediate monocyte phenotype, the monocytes can promote tumor cell resistance to cytotoxic killing by DOX, thus demonstrating a cross-talk between monocyte and tumor function. We found that in an environment of monocyte/tumor cross talk, arginase I expression is further increased in a cytotoxic environment. Together, this data demonstrates an active cross talk between monocytes and tumors resulting in multiple mechanisms of tumor resistance to chemotherapy. Disclosures: No relevant conflicts of interest to declare.

Abstract Autologous stem cells transplant in tandem is considered the standard therapy for patients with Multiple Myeloma (MM) and Primary Amyloidosis. The collection as well as the infusion of stem cells, which are preserved in dimethyl sulfoxide (DMSO), may cause serious side effects including renal failure. We reviewed the charts of MM patients undergoing stem cell transplant from 2001 through the end of 2005. Patients were grouped into one of 3 categories: Amylodosis, MM with Immunoglobulin G (IgG) and MM with non IgG. Creatinine and creatinine clearance values were collected 14 days prior to, the day of, 3 days post, and 28 days post infusion. The volume of the transplant as well as the number of CD 34+ stem cells reflect the dose of DMSO infused since all the cryopreservation of cells were done with 105 DMSO solution. We also collected data about the administration of nephrotoxic agents such as Aminoglycoside antibiotics, Vancomycin and Amphotercin B because these patients are at increased risk of developing infections. We also reviewed the dose of consolidation chemotherapy (Melphalen) as a potential nephrotoxic agent. Chi-square analysis was used. 645 patients were included [380 (58.82%) males and 265 females (41.18%)]. 384 received Vancomycin, 7 received Gentamycin and 8 received Amphotericin B with total of 146 missing data. 191 (29.57%) had Amyloidosis, 285 (44.12%) IgG MM and 169 (26.32%) non IgG MM. Only 6 transplants were allogeneic. The dose of Melphalen ranged between 0–200 mg/m2 over 2 days at the discretion of the physician. The mean weight was 82.25 Kg and median weight was 81.8 Kg. The mean age 57.12 years and median age was 58 years. 608 patients (94.12%) had one transplant, 35 (5.42%) had 2 transplants and 3 (0.46%) had 3 transplants. The mean volume was 289.20 ml and median volume was 245 ml. The mean number of CD34+ cells was 5.39 × 10(6)/kg with a median of 4.74 × 10(6). The mean and median Creatinine levels were 1.26 mg/dl and 1 mg/dl respectively at 2 weeks prior to transplant, 1.23mg/dl and 1mg/dl on the day of transplant, 1.18 mg/dl and 1mg/dl at 3 days after transplant and finally 1.16mg/dl and 0.9mg/dl at 4 weeks interval. 67 males as well 50 females had renal failure prior to transplant but there was no statistical difference due to gender (p 0.001). Creatinine clearance levels were 83.96 ml/min at 2 weeks prior, 83.84 ml/min at day zero, 88.57 ml/min and 91.89 ml/min respectively. The median were 83.37 ml/min, 82.77 ml/min, 86.43 ml/min and 91.29 ml/min respectively. Even though 35 creatinine values were missing within the first 3 days period, there was no acute renal failure (ARF) (0.5 mg/dl increase) noted with a 95% C.I. 95% in 494 patients with normal creatinine. The creatinine level improved in 93 patients with an abnormal level and only 24 were left with abnormal levels. This might represent a dilutional effect due to fluid administration during the transplant. Concerning the incidence of chronic renal failure (CRF) at 4 weeks interval, considering that only 47 laboratory values were missing the results was as follows: 4 patients had > 0.5 mg/dl creatinine increase from the 485 normal patients with C.I. 95%. CRF was still observed in 38 patients of the 72 patients with baseline renal failure. Even though 9 had very poor creatinine clearance <10ml/min (p 0.01) only 5 were left with severe creatinine clearance after transplant (p 0.05) We found that DMSO does not induce ARF or an exacerbation of CRF in transplants patients for Amyloidosis and Multiple Myeloma.

Abstract Background: High dose therapy with autologous stem cell transplantation (HDT-ASCT) has prolonged survival in patients with multiple myeloma. Patients who achieve a complete response (CR) benefit the most from this form of therapy. Thus, achieving a CR is an important goal of therapy and it will be beneficial if the probability of achieving CR can be determined for any patient before transplant. Patients and Methods: A large cohort of patients with myeloma who received HDT-ASCT at Mayo Clinic Rochester was studied. The impact of various demographic, clinical and laboratory characteristics relating to the patients and their disease acquired were studied for their impact on response to HDT-ASCT, especially CR. Patients with a serum M-protein <0.1g/dL were excluded. Response definitions were as defined by established criteria. Survival analysis was performed according to the Kaplan-Meier method while univariate and multivariate analyses were performed with the proportional hazards method. We utilized knowledge of the rate of M-protein production by myeloma cells together with the clearance of the protein to estimate the pre-transplant disease burden. Results: We studied 224 patients with a median age of 56.5 years (32.6 – 71). Patients were transplanted a median of 8.7 months after diagnosis. Almost all patients had a response to HDT-ASCT and 78 (35%) achieved a CR. Those patients who achieved a CR had a longer time to progression (TTP) compared to those who did not achieve CR (Figure 1). The cohort was thus divided into two groups: patients who achieved CR and those that did not. The clinical and laboratory characteristics of the two groups were compared. Among the pre-transplant parameters tested, only the size of the serum M-spike was a predictor for CR (p<0.0001). A simple function that describes the probability of achieving CR based on the serum M-spike before HDT-ASCT is described. The estimated rate of tumor re-growth after HDT-ASCT in patients who obtain a CR and in patients who only get a partial response are presented. Conclusions: The pre-transplant disease burden in myeloma is the main determinant of response to HDT-ASCT. The individual probability of achieving CR can be estimated from simple clinical parameters providing a quantitative risk assessment prior to such a high-risk procedure. There is significant expansion of myeloma cells after HDT-ASCT. The design of clinical trials may benefit from knowledge of the kinetic aspects of the disease. Figure Figure

Abstract Abstract 1178 Poster Board I-200 Background: High-dose chemotherapy with autologous peripheral blood stem cell transplantation (PBSCT) has been shown to be of value in selected patients with malignant lymphoma and multiple myeloma (MM). Both granulocyte macrophage colony stimulating factor (GMCSF) and granulocyte colony stimulating factor (GCSF) are widely used following stem cell transplantation to support accelerated myeloid recovery and potentially shorten hospital stay. In the recent years, PBSCT is increasingly done in an ambulatory care setting and it is not clear if routine growth factor use has any potential benefit. We undertook this study to compare engraftment kinetics, incidence of febrile episodes, hospitalization duration and other outcomes among transplants done with or without growth factor support Patients and Methods: We included adult patients undergoing PBSCT for myeloma and lymphoma between May 2007 and June 2009 in an ambulatory care setting. Prior to April 2008 (Group-1) all patients received GMCSF 500 mcg/ day starting on day 6 routinely. Since April 2008, there was a shift in clinical practice and routine use of GMCSF was discontinued due to lack of clear evidence regarding benefit. Patients transplanted between April 2008 and June 2009 did not routinely receive GMCSF (Group-2). Typical conditioning regimen for lymphoma was BEAM (BCNU, Etoposide, Cytosine Arabinose, Melphalan) and for multiple myeloma was melphalan 200mg/m2. Patients' demographics details, indication for PBSCT, duration of neutropenic fever, hospital stay, and neutrophil and platelet engraftment were collected from electronic medical records. Neutrophil engraftment is defined as the first day of 2 consecutive days when ANC was > 0.5 × 109/L and platelet engraftment is defined as first of 7 consecutive days on which patient's unsupported platelet count was greater than 20× 109/L. Results: A total of 309 were included in this study, 126 (40%) patients in group-1 (69 with MM, 57 with lymphoma) and 183 (60%) in group-2 (100 with MM, 83 with lymphoma). In group-1, 73 (58%) and in group-2 130 (71%) were male patients. Median age was 59 (29-74) years in group 1 and 58 (24-76) years in group-2. Patients in group 1 received a median of 3.65 (1.1-8.7) versus 4.37 (1.1-9.54) CD34+ x106/kg in group 2 (P =0.005). Median time to neutrophil engraftment was 12 (95% CI 12, 12) for group-1 and 14 (95% CI; 13-14) for group-2 (Kaplan Meier analysis; log rank P < 0.0001). Median estimated time to platelet engraftment was 14 days (95% CI; 13, 15) for group 1 and 13 days (95% CI; 13-13) for group 2 (Kaplan Meier analysis; log rank P 0.007). In group-1 98 (78%) patients developed febrile episodes compared to 117(64%) in group-2 (P = 0.009). Median duration of fever was 2 days (range, 1-8) in group-1 compared to 1 day (range, 1-8) in group-2 (P = 0.0003). The median (range) duration of hospital stay was 7 (1-40) days for group-1 compared to 8 (2-56) days for group-2 (P=NS). There was no significant difference in mortality between these two groups. Conclusion: Routine use of granulocyte growth factors is associated with a shorter time to neutrophil engraftment, but associated with a delay in platelet engraftment. The longer time to neutrophil engraftment without growth factor use does not translate into any increase in frequency of febrile episodes. On the contrary, higher number of febrile days is seen with use of growth factors, likely explained on the basis of drug fever. No difference in the frequency of engraftment syndrome or treatment related mortality was seen. Disclosures: No relevant conflicts of interest to declare.

Abstract Background: Patients with AL and congestive heart failure have a median survival of less than one year. Methods: Between 1994 and 2005, 11 patients underwent sequential heart transplant followed by autologous peripheral blood stem cell transplant (SCT) for treatment of AL. Patients had heart dominant AL with minimal/no other organ impairment and no evidence of multiple myeloma. Results: Patients ranged in age from 35 to 63 years (median 54). All had biopsy proven amyloidosis and monoclonal protein detectable in serum (73%) or urine (100%). Free light chain assay was available prior to SCT in 6 and was abnormal in all. All patients presented with NYHA Class III or IV heart failure. All but two patients had no other organ involved at the time of heart transplant. One patient had his heart transplant at another facility and had renal involvement at the time of heart transplant. One patient had peripheral nerve involvement documented prior to heart transplant. Five patients had progression of amyloid to involve other organs by the time of SCT. These included: renal (6), peripheral nerve (2), macroglossia (3), gastrointestinal (2). The median time from diagnosis to heart transplant was 3 months (range 1 to 5). The median time from heart transplant to SCT was 8 months, (range 3 to 24). Conditioning chemotherapy consisted of melphalan 200 mg /m2 (6 patients) or melphalan 140 mg/m2 (5 patients). Two patients died of complications before day +100, (TRM of 18%). Hematologic remissions were seen in 8 and organ responses in 3. Five were unable to be evaluated for organ response due to the heart transplant. Three died from progressive amyloidosis at 66, 56.7, and 55 months following SCT. The median survival is 56.7 months from SCT. Six are alive with a median follow-up of 24 months, range 9 to 90 months. Among the 6 surviving patients, one patient relapsed and one patient has failed to improve, but 4 patients are in continued remission. One patient developed secondary myelodysplastic syndrome. Conclusions: Heart transplant followed by SCT is feasible and offers durable remissions for carefully selected patients with cardiac AL. Figure Figure

Abstract Background: Autologous stem cell transplantation (SCT) improves survival in patients (pts) with multiple myeloma (MM). We have previously demonstrated that the degree of response at transplant does not impact on the outcome of transplant. However, newer induction regimens such as thalidomide and dexamethasone (Thal-Dex) result in higher response rates compared to previously used regimens such as single agent dexamethasone or vincristine, doxorubicin, and dexamethasone (VAD). We examined the outcome of SCT following three different induction therapies for newly diagnosed MM, namely VAD, single agent Dex, and Thal-Dex. Patients and Methods: 340 patients with MM who received their SCT within 12 mos of diagnosis (median 5.8, range 3–12) were studied. Patients receiving more than one induction therapy as well as those in whom thalidomide was added to dexamethasone for lack of response were excluded from the analysis. There were 105 pts in the VAD group, 140 in the Dex group and 95 in the Thal-Dex group. Responses were defined using standard criteria. Results: The study cohort consisted of 209 males (59%), with a median age of 57 years (range 30–76) at transplant. Baseline characteristics were similar in the 3 groups, except for lower age in the VAD group (median 55.8) compared to Dex (59.6) and Thal Dex (57.4) and shorter time to transplant in the Dex group (5.4 m) compared to VAD (6.4) and Thal Dex (5.9). Markers of disease activity pre-transplant, including B2M and marrow plasma cell percentage were higher in the Dex group compared to either VAD or Thal Dex. The proportion of patients with any response to induction therapy was lower in the Dex group compared to the other two. All pts in the Dex and the Thal-Dex groups received melphalan only conditioning compared to 70% in the VAD group, the rest receiving Melphalan/TBI. An objective response was achieved after SCT in 96%, 97%, and 98% of pts in the VAD, Dex and Thal-Dex groups respectively (P=0.8). A complete response to SCT was seen in 49% of patients in VAD group, 45% among those in the Dex group and 38% among those in the Thal Dex group (P=0.38). There was no difference in the median progression free survival after transplant (P=0.21) or overall survival from diagnosis (P=.34) between the three groups. The proportion free from progression at 2 years post transplant was 54%, 55% and 46% for Dex, VAD and Thal-Dex respectively. The proportion surviving at 4 years from diagnosis was 64%, 65.4% and 72% respectively for the three groups. Conclusion: We did not observe any difference in the response rates including complete responses to SCT in the three groups with nearly all pts in each group achieving a response. The progression free survival and overall survival appear to be comparable between the three groups. The results from initial therapy cannot be compared between the three regimens since the study population is restricted to patients reaching stem cell transplant. Within the limits of the study, there does not appear to be any long term impact of the initial therapy for the patients going onto an early stem cell transplant. Figure Figure

INTRODUCTION The use of growth factors filgrastim and sargramostim are associated with often dramatic degrees of fluid retention in patients with amyloidosis who have coexistent cardiac involvement or nephrotic syndrome. Significant degrees of fluid retention can complicate the post transplant management of patients with AL receiving high dose chemotherapy. We report outcomes in a cohort of amyloidosis patients who received no growth factor support post transplant. PATIENTS AND METHODS 283 consecutive patients seen for stem cell transplant are included in this cohort. In order to be considered evaluable for engraftment the patient must have survived for 30 days or was excluded from analysis. All patients had biopsy verified AL. Patients also had to have visceral organ dysfunction in order to be eligible for stem cell transplant with a minimum of one visceral organ involved. RESULTS Among 283 patients transplanted, 244 were evaluable for engraftment. There were 145 men (59%). Renal involvement was present in 163 (67%), cardiac involvement by echocardiography in 47%, hepatic involvement in 16%, and peripheral nerve involvement in 11%. The median age was 56.6 years (range 33–73). The median time from diagnosis of amyloidosis to stem cell transplantation was 4.2 months. A neutrophil count of 500/uL was achieved in 50%, 75%, and 90% of the total group at 14, 16, and 22 days respectively (figure 1). A platelet count of 20,000/uL was achieved in 50%, 75%, and 90% of patients at 14, 19, and 28 days respectively (figure 2). A platelet count of 50,000/uL was achieved in 50%, 75%, and 90% of patients at 18, 28, and 52 days respectively. The median time spent in the hospital for the entire cohort 9 days. 46 of the patients (19%) completed the entire procedure as an outpatient. 75% of patients were discharged within 18 days and 90% were discharged within 32 days. 137 patients were blood culture negative throughout the entire procedure (56%). A blood culture was positive in the remaining 107 patients. 68 of these 107 contained a culture for Staph. coagulase negative. 39 (16%) had bacteremia associated with other organisms. CONCLUSION Transplantation of patients with amyloidosis without using growth factor is feasible. The median time to achieve neutrophil and platelet counts of 500 and 20,000/uL respectively is 14 days. It is reasonable to withhold growth factor from AL patients undergoing stem cell transplantation. Figure Figure Figure Figure

Abstract Background: Renal insufficiency of varying severity including end stage renal disease requiring dialysis is often a presenting manifestation of multiple myeloma (MM). While many patients (pts) improve following initiation of therapy for MM, a considerable number of pts proceed to stem cell transplant with less than optimal renal function. It is not clear whether the outcome of their transplants differs from pts with normal renal function. Methods: The MM transplant database was searched to identify pts with a Creatinine clearance (Crcl) of less than 50 ml/min/m2 (study cohort). These pts were then matched to two pts each with a clearance of ≥ 50 ml/min/m2 (control cohort), based on cytogenetic abnormalities (normal vs. abnormal), circulating plasma cells (yes vs. no), age at transplant, % of plasma cells at transplant, plasma cell labeling index, time to transplant from diagnosis and the disease status at transplant, the factors used in that order of importance. Results: Eighty pts with a Crcl < 50 ml/min were identified and matched to 160 pts with Crcl ≥ 50 ml/min. The pts were matched for the above factors and the two groups were similar in terms of their other baseline features except CRP and B2M, both of which were lower in the control group. Pts with reduced renal function were more likely to receive dose reduced melphalan for conditioning (32.5%) compared to the control group (2%; P < 0.0001). The outcomes from the stem cell transplant were similar in both the groups. 96% of pts obtained an objective response to stem cell transplant in each of the groups with no difference in the time to response; and a complete response was seen in 38.5% and 36.6% of the study and control cohorts respectively (P=NS). The median post transplant progression free survival was 18.2 months and 18.4 mos respectively for the study cohort and the control group (P=0.4). However, the median overall survival from transplant was shorter for the study cohort (30.7 mos vs. 60 mos for the controls; P = 0.007; Figure). The time to platelet and neutrophil engraftment was not different between the groups. In terms of transplant related toxicity, the median days hospitalized was higher in the study group (5 days vs. 9.5 days; P=0.003) as was the incidence of grade 3 and 4 mucositis (8% vs. 23%; P= 0.0008). Six pts (7.5%) had treatment related deaths in the study group compared to 3 pts (2%) among the controls (P=0.03), the majority of the deaths being infection related. Conclusion: Here we demonstrate that pts with MM and reduced renal function derive disease free survival comparable to those with normal renal function, despite the increased use of reduced dose Melphalan for conditioning. The toxicity is clearly increased in the presence of abnormal renal function. Interestingly, the overall survival was inferior among the pts with reduced renal function. One possible explanation for this observation is the decreased availability of novel therapies for salvage among pts with reduced renal function as many of them would not be eligible for clinical trials due to reduced renal function. Figure Figure

Abstract Background: Immune editing is a major mechanism used by tumors to promote its survival. We have reported previously the presence of a novel phenotype of immunosuppressive monocytes (CD14+HLA-DRlow/neg) in a number of cancers. Increased presence of these cells was associated with decreased treatment response and OS. We have demonstrated that certain tumor cells can convert normal CD14+HLA-DR+ monocytes to CD14+HLA-DRlow/neg phenotype in an IL-10 independent and a tumor specific way. These CD14+HLA-DRlow/neg monocytes, in turn, protect tumors from cytotoxic killing from chemotherapy. Here we report up-regulation of heat shock protein-27 (HSP27) as one mechanism mediating this effect. Method: Monocytes from healthy donors were co-cultured with lymphoma cell lines (OCI-Ly3, Jeko-1, and Granta-519) with or without doxorubicin (DOX). Cultured cells were assessed for phenotype, viability and proliferation by flow cytometry. Lymphoma cells were isolated with anti-CD19 immunomagnetic beads and assayed by immunoblot for expressions of proteins regulating apoptosis. HSP27 levels in human plasma were measured by ELISA. Results: DOX incubation induced apoptosis and decreased viability of all three cell lines; and co-culture with monocytes improved the lymphoma cell survival (for example, untreated Granta-519 had a 2.1±0.45 fold expansion, that was reduced to 0.39±0.12 when treated with DOX and 0.81±0.27 after co-culture with monocytes with DOX. p<0.05, n=11.) Co-culture with monocytes induced increased HSP27 expression in lymphoma cells. HSP27 levels were further increased in co-culture with monocytes and DOX, with corresponding decrease in cleaved Caspase-3 levels. As tumor cells can secrete HSP27, we found detectable levels of HSP27 in plasma of lymphoma patients. Increased HSP27 in plasma correlated with increased proportion of CD14+HLA-DRlow/neg monocytes in blood. Conclusions: We have found that monocytes may promote lymphoma resistance to DOX killing by inducing increased HSP27. In turn, HSP27 from lymphoma patients may induce immune suppressive phenotype in monocytes. Together, this data demonstrates an active cross talk between monocytes and lymphoma resulting in multiple mechanisms of tumor resistance to chemo-immunotherapy. Disclosures No relevant conflicts of interest to declare.

Abstract Background: Little data exists on the incidence rate of transfusion reactions and red cell antibody formation following allogeneic (allo) hematopoietic progenitor cell transplant (HPCT) recipients. Study Design and Methods: Consecutive related and unrelated Allogeneic HPCTs from 2006 to 2013 were retrospectively reviewed regardless of graft source. Allo HPCT recipients were analyzed as a whole as well as divided into ABO compatibility groups of identical, minor mismatch, and major/bidirectional mismatch. Transfusions, transfusion reactions and antibodies were analyzed for the first year post-transplant while survival was recorded throughout the available follow-up period. Results: During the study period, 573 patients ranging in age from 0.6 to 72 years underwent first allo HPCT for various malignant and non-malignant etiologies: 278 acute leukemias, 89 lymphomas, 40 multiple myelomas, 134 other hematologic malignancies, 32 non-neoplastic etiologies. Of these, 52% underwent myeloablative conditioning and 48% reduced intensity conditioning. Transfusion reactions were reported in 93 of the 573 allo HPCT recipients. The incidence rate of transfusion reactions per 10,000 transfusion episodes was 45.54 in the ABO identical, 61.28 in the minor mismatch, and 29.95 in the major mismatch groups (p=0.04). The most common reaction type reported in all groups was allergic followed by febrile non-hemolytic, transfusion associated circulatory overload, and delayed hemolytic or serologic reactions. No acute hemolytic, transfusion related acute lung injury (TRALI), post transfusion purpura, transfusion associated graft-versus-host disease, or transfusion associated sepsis reactions were reported. A total of 43 unique patients(7.5%) developed new antibodies post-transplant: 16 allo HPCT recipients developed clinically significant antibodies, 17 developed clinically insignificant antibodies, and 17 developed auto antibodies post-transplant. Including those patients with pre-transplant antibodies the overall prevalence of red blood cell antibodies was 14.5%. See Table 1 for incidence rate for forming new rbc antibodies post-transplant. Table 1. New RBC Antibody Formation Incidence Rate Post-Transplant ABO Compatibility Group Clinically Significant Antibody Incidence /10,000 RBC Transfusions Clinically Insignificant Antibody Incidence/ 10,000 RBC Transfusions, Auto Antibody Incidence/10,000 RBC Transfusions Total Antibody Incidence/10,000 RBC Transfusions Identical 39.33 16.85 39.33 95.51 Minor Mismatch 35.87 57.39 43.04 136.30 Major Mismatch 8.34 16.67 8.34 33.35 A statistically significant difference (p=0.001) was seen in total antibody incidence when comparing the ABO compatibility groups. The most common, clinically significant allo antibodies formed were Anti-E, Anti-Jka, Anti-A1, Anti-K, Anti-D, and Anti-C. Survival of allo HPCT recipients as a whole was not statistically different for those who formed new rbc antibodies post-transplant following adjustment for ABO compatibility, age at transplant, diagnosis, graft source, and pre-transplant rbc infusions (p=0.068). Allo HPCT recipients that formed new rbc antibodies were not shown to have prolonged engraftment. Engraftment, neutrophils (ANC) and platelets (PLT), were not statistically different (p=0.34 ANC; p=0.20 PLT) when comparing all allo HPCT recipients to those who formed a new rbc antibody. Conclusion: Transfusion reaction and rbc antibody incidence rates were higher in the ABO minor mismatch when compared to the ABO identical and ABO major mismatch groups. The reaction etiology (predominantly antibody mediated) and the formation of new antibodies indicates a surprisingly active humoral immune system. The overall prevalence of antibody formation is likely affected by high exposure to transfusions. Development of a new rbc antibody did not affect engraftment or survival outcomes. Disclosures No relevant conflicts of interest to declare.