Witzig, Thomas E.

Background: High dose chemotherapy and autologous stem cell transplant (SCT) remains the preferred therapy for eligible patients with multiple myeloma (MM). Several studies have demonstrated an improvement in median survival with use of SCT. Patients with myeloma may undergo SCT immediately following 4–6 cycles of ‘induction’ therapy or at the time of relapse from the initial plateau phase. Available evidence does not suggest a survival difference between the two approaches. Methods: We retrospectively evaluated our experience with autologous single SCT for MM to compare the results of delayed SCT to early SCT. We identified from our transplant database, 202 patients with MM, who underwent SCT between October 1992 and November 2002. 101 patients, who responded to induction chemotherapy, had stem cells collected in plateau phase, received maintenance chemotherapy and had SCT at the time of first relapse (delayed SCT group). The remaining 101 patients, after initially achieving a response underwent upfront SCT (early SCT group). Patients refractory to initial therapy were excluded from this study. Most of the early transplants were done in the recent years and hence this group has a shorter follow up. Results: The study cohort had a median age of 55 years (range 29 – 72) at diagnosis consisting of 126 males (62%), with no significant demographic difference between the two groups. As expected measures of tumor burden (M protein, B2M and marrow plasma cell percentage) were significantly higher in the delayed group. Plasma cell labeling indices and presence of abnormal cytogenetics were higher in the delayed SCT group as well at transplant. TBI containing regimens were used more often in the delayed group reflecting a difference in the time periods of transplant. There was no difference between the groups in terms of overall response to transplant though complete response rate was higher for the early transplants. (Table). There was no difference in the time to overall response between the groups (P=0.13, Kaplan Meier estimate). Though the median progression free survival (PFS) from transplant was shorter for the delyaed SCT group, the overall survival (OS) from diagnosis of MM was comparable for the two groups (Table). The overall survival estimate at 5 year from diagnosis was 60% for both groups. Conclusions: Review of our experience demonstrates comparable overall survival for an early SCT compared to SCT at the time of relapse. Although there is an advantage for early SCT in terms of more chemosensitive disease as shown by a longer PFS from SCT, there is no benefit in OS from time of diagnosis. Patient preference and other co-morbidities should play a role in the decision regarding timing of transplant. This study has the disadvantage of being retrospective in nature and the two groups being spread over different periods in time. Early (n=101) Delayed (n=101) P Overall Response 100 (99%) 94 (94%) 0.07 Complete Response 43 (42%) 28 (27%) 0.04 Median PFS (From Transplant) 26.7 months 14.8 months <0.0001 Median OS (From diagnosis) 67 months 70 months 0.1

Abstract Despite advances in treatments for patients with non-Hodgkin’s lymphoma (NHL), the relapse rates remain high and 40% of diffuse large B-cell NHL (DLBCL) patients die of disease. New therapies to augment the host anti-tumor immune response are needed. Reports of graft-versus-lymphoma responses in patients who have received allogeneic hematopoietic cell transplant indicate a role for cellular immunotherapy. However, these patients have variable levels of immunodeficiency which may impact the efficacy of cellular therapy. To study this we first evaluated the cellular immune status of patients with relapsed NHL. Proliferation of peripheral blood mononuclear cells (PBMNC) stimulated with anti-CD3/CD28 beads was reduced by more than 3.5 folds for patients with DLBCL (n = 3) compared to that of age-matched healthy donors (n = 5; p = 0.02). Removal of monocytes from PBMNC by use of anti-CD14 immunomagnetic beads restored proliferation to that of healthy donors. Further, monocytes from these patients were deficient in stimulating allogeneic T cell proliferation by 3 folds compared to monocytes from healthy donors (n = 3 NHL; n = 8 normal; p < 0.01). Peripheral blood from 12 NHL patients (9 DLBCL; 1 grade 3 follicular lymphoma; 2 composite) and 12 age-matched healthy donors were characterized by flow cytometry to determine the phenotype of these suppressive monocytes. There was no difference in the % monocytes in the blood between NHL patients and healthy donors; however, NHL patients had elevated % monocytes with a suppressive phenotype (CD14+HLA-DRneg) compared to normals (NHL 38.9 ± 4.93%; normal 8.3 ± 2.15; p < 0.0001). This phenotype is distinct from other myeloid suppressors (Lin-CD33+HLA-DR-) or non-classical monocytes (CD16+), neither of which was different in numbers between NHL and normal donors. This suggests that the CD14+HLA-DRneg monocytes are responsible for the observed T cell suppression. To further characterize the function of these cells, we cultured purified CD14+ monocytes from NHL and compared their differentiation capacity with those from normal donors. The percentage of CD14+HLA-DRneg monocytes in initial ex vivo culture was inversely correlated with the percentage of pure, mature dendritic cells (mDC) generated with TNF-a and PGE2 as maturation factors (CD80+CD83+; n = 9; p = 0.015). As CpG oligonucleotides are also capable of immune stimulation and have some anti-tumor activity in clinical trials, we investigated the effect of CpG on mDC differentiation in NHL. In healthy donors, maturation of monocytes with CpG yielded highly pure mDC (90.7 ± 2.15%, n = 3). However, preliminary results of mDC yield from monocytes of NHL patients matured with CpG was only 22.6 ± 11.2% (n = 2). This data suggests alternative signaling pathways of these suppressive monocytes. Preliminary analysis of a proteome array for 46 kinase phosphorylation sites from 37 proteins in 2 NHL and 3 healthy donors suggest changes in phosphorylation of 17 protein kinases for CD14+HLA-DRneg compared to CD14+HLA-DR+ cells. Functional correlation of these protein kinase phosphorylation changes is needed to definitively target the pathway characteristic of CD14+HLA-DRneg monocytes. Finally, we have identified a serum-free culture method that can consistently generate highly pure mDC from monocytes of NHL patients (93.0 ± 3.6%, n = 9) and is readily adaptable to good manufacturing practice for clinical use in immunotherapy. Taken together we have described for the first time a population of CD14+HLA-DRneg monocytes that is a significant source of immunosuppression in NHL patients and are beginning to target methods of overcoming this suppression.

Abstract Abstract 587 Background: The phosphatidylinositol 3-kinase/mammalian target of rapamycin (mTOR) signal transduction pathway controls cell proliferation and survival. Everolimus is an oral agent targeting raptor mTOR (mTORC1). The trial's goal was to determine the anti-tumor activity and safety of single-agent everolimus in patients with relapsed/refractory Waldenstrom's macroglobulinemia (WM). Patients and Methods: Eligible patients had measurable disease (IgM monoclonal protein >1000 mg/dL with >10% marrow involvement or nodal masses >2 cm), a platelet count ≥75,000 × 106/L, a neutrophil count ≥1,000 × 106/L, and a creatinine and bilirubin ≤2x laboratory upper limit of normal. Patients received everolimus 10 mg PO daily and were evaluated monthly. Tumor response was assessed after cycles 2 and 6 and then every 3 cycles until progression. Results: 50 pts were treated. The median age was 63 years (range, 43-85). The overall response rate (CR+PR+MR) was 70% (95% CI: 55-82%), with a PR of 42% and 28% MR. The median duration of response and median progression-free survival (PFS) has not been reached. The estimated PFS at 6 and 12 months is 75% (95%CI: 64-89%) and 62% (95%CI: 48-80%), respectively. Grade 3 or higher related toxicities were observed in 56% of patients. The most common were hematological toxicities with cytopenias. Pulmonary toxicity occurred in 10% of patients. Dose reductions due to toxicity occurred in 52% of patients. Conclusions: Everolimus has high single-agent activity with an overall response rate of 70% and manageable toxicity in patients with relapsed WM, and offers a potential new therapeutic strategy for this patient group. Disclosures: Ghobrial: Millennium: Honoraria, Research Funding, Speakers Bureau; Celgene: Consultancy, Honoraria, Speakers Bureau; Novartis: Honoraria, Speakers Bureau. Gertz:celgene: Honoraria; millenium: Honoraria, Membership on an entity's Board of Directors or advisory committees. Richardson:Millennium Pharmaceuticals, Inc.: Consultancy, Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Celgene: Consultancy, Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Johnson and Johnson: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Novartis: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Keryx: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; BMS: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau. Treon:Millennium: Honoraria, Research Funding, Speakers Bureau; Celgene: Honoraria, Research Funding, Speakers Bureau; Genentech: Honoraria, Research Funding, Speakers Bureau. Witzig:Novartis: Research Funding.

Abstract Purpose: Primary colorectal large B-cell lymphoma is rare and accounts for less than 1% of all malignancies in the colon. Standard treatment for limited stage diffuse large B-cell lymphomas (DLBCL) includes systemic therapy combined with involved field radiation therapy. However, radiation therapy may often not be feasible in patients with primary colon lymphoma. For primary DLBCL of the colon particularly the cecum, surgical resection prior to the administration of systemic chemotherapy has been considered to improve local control. The goal of this study was therefore to determine whether surgical resection improves the outcome of patients with primary DLBCL of the colon. Methods: Clinical information and outcomes on all the patients with primary DLBCL of the colon seen at Mayo Clinic, Rochester, between January 1980 and June 2005 were retrospectively reviewed. Results: There were 28 patients identified with primary colon DLBCL. Pre-existing conditions like colon polyps, Crohn’s disease and diverticulosis were uncommon. The most common presenting symptom was bleeding per rectum seen in 13 patients (46.5%). Other symptoms included abdominal pain, diarrhea and anemia. All patients had early stage disease (stage1–22 patients, stage2–6 patients) at diagnosis. Of the 28 patients, 16 underwent initial surgery followed by chemotherapy, 7 were treated with chemotherapy alone, and 5 patients had inadequate data to determine time to progression or overall survival. Chemotherapy was anthracycline based, with the most common regimen being CHOP (Cyclophosphamide, Doxorubicin, Vincristine, Prednisone). There was no difference in overall survival or time to progression between the 16 patients who received combined modality therapy compared to the 7 patients who received chemotherapy alone. Of the 16 patients who underwent surgical resection followed by chemotherapy, all 5 patients who relapsed, relapsed at other sites in the colon. Conclusion: Surgery as part of combined modality therapy did not appear to improve the outcome of patients with primary DLBCL of the colon. Systemic chemotherapy with an anthracycline-based regimen in combination with rituximab is therefore likely to be sufficient treatment for these patients. Follow-up for these patients should include a colonoscopy to monitor for recurrences at other sites in the colon.

Abstract The objective of this study was to analyze molecular changes that occur at the protein level in WM and IgM-MGUS in order to identify proteins dysregulated at disease progression and design new therapies. We employed antibody protein microarrays (BD Clonetech, CA) to measure changes in the patterns of protein expression between WM, IgM-MGUS and normal lymphoplasmacytic cells as control. The antibody array is a novel technique that assays protein differences directly by hybridizing fluorescently labeled protein mixtures from cell extracts onto a glass slide spotted with 512 different monoclonal antibodies specific for human proteins. CD 19+ and CD138+ purified lymphoplasmacytic cells were obtained from cryopreserved bone marrow samples of 5 newly diagnosed patients with WM and 5 patients with IgM-MGUS. Control plasma cells were obtained from 3 pooled CD19+ and CD138+ purified normal donor bone marrow cells. To assess differential expression, the mean of the ratios of Cy5/Cy3 for each sample were analyzed using the Clontech software to calculate an internally normalized ratio. The normalized data were analyzed by the Genespring software and changes of protein expression ≥2 fold in 60% of the samples as compared to normal control were identified in both WM and MGUS groups. There were 20 proteins upregulated in WM and 21 proteins in MGUS as compared to normal control cells These included proteins from the small GTPases such as the Ras, Rho and Ran families (Rab 4, MONA, RCC1, and CDC42GAP), Kinases/signaling proteins (ROK alpha, p62 dok, JAK, 14-3-3e), cyclin dependent kinase (CDK2), fatty acid synthase (HDAC3), NFkB pathway (IKKalpha, IKBe), and histone deacetylase. The WM and IgM MGUS differed in only 3 proteins using the 2-fold threshold. The WM samples showed overexpression of the heat shock protein Hsp90, the Ras family protein CDC25C, and the chemotaxis protein p43/EMAPII as compared to the MGUS samples. This is the first proteomic study of WM and MGUS patients. It identifies novel proteins dysregulated in WM that may serve in future clinical trials as targets for therapy such as Hsp90, NFkB, HDAC and fatty acid synthase. In addition, it identifies 3 proteins that identify disease progression from MGUS to WM, which could be useful for monitoring MGUS patients and designing targeted therapies to prevent progression to WM.

Abstract Numerous clinical therapies have attempted to modulate tumor cell immunity, but for the most part, have proven unsuccessful. The inability to produce or augment an effective immune response is due in part to regulatory T (Treg) cells, which inhibit CD4 and CD8 T cell function. Our group has recently shown that Treg cell numbers are elevated in NHL tumors and that NHL B cells induce the development of Treg cells thereby inhibiting anti-tumor responses. The ability of NHL B cells to direct the cellular composition of their microenvironment is critical to our understanding of tumor immunity and we therefore wanted to determine if NHL B cells also directed the expansion or reduction of other T cell populations. IL-17-secreting CD4+ T cells (TH17), a newly characterized CD4+ T helper cell lineage, promote inflammation and play an important role in autoimmune disease. IL-17 has been shown to inhibit tumor cell growth suggesting a potential role for TH17 cells in anti-tumor immunity. We therefore set out to determine if TH17 cells were present in NHL tumors and whether or not their numbers were regulated by NHL B cells. Using unsorted mononuclear cells from malignant lymph nodes, we were unable to detect IL-17 expression in resting CD4+ T cells or CD4+ T cells activated with PMA/Ionomycin stimulation (less than 1%). However, IL-17-secreting CD4+ T cells could be detected in significant numbers in inflammatory tonsil and normal PBMCs. Interestingly, depletion of CD19+ NHL B cells from mononuclear cells obtained from patient biopsies resulted in detection of a clear population of IL-17-secreting CD4+ T cells (5%). These results suggest that NHL B cells suppress TH17 cell differentiation. The frequency of IL-17-secreting CD4+ T cells could not be further enhanced by the addition of exogenous TGF-b and IL-6, a cytokine combination favoring for TH17 differentiation, suggesting a further impairment of TH17 cell differentiation in the tumor microenvironment. In contrast, Foxp3 expression could be detected in resting CD4+ T cells (30%) and could be induced in CD4+CD25−Foxp3− T cells activated with TCR stimulation (28%). Contrary to the inhibition of TGF-b-mediated TH17 differentiation, Foxp3 expression could be dramatically upregulated by TGF-b in intratumoral CD4+ T cells (35%). In addition, lymphoma B cells strongly enhanced Foxp3 expression in intratumoral CD4+CD25−Foxp3−. Furthermore, when added together, the frequency of Foxp3+ T cells and Foxp3-inducible cells reached up to 60% of CD4+ T cells in tumor microenvironment of B-cell NHL. These findings suggest that the balance of effector TH17 cells and inhibitory Treg cells is disrupted in B-cell NHL and significantly favors the development of inhibitory Treg cells. Our data indicate that lymphoma B cells are key factor in regulating differentiation of intratumoral CD4+ T cells toward inhibitory CD4+ T cells.

Abstract Background: The phosphatidylinositol 3-kinase/mammalian target of rapamycin (mTOR) signal transduction pathway integrates signals from multiple receptor tyrosine kinases to control cell proliferation and survival. Everolimus (RAD001, Novartis Pharmaceuticals) is an oral investigational antineoplastic agent that targets mTOR. Objectives: To learn the anti-tumor activity and toxicity of single-agent RAD001 in pts with relapsed/refractory aggressive NHL. Patients and Methods: Patients were eligible if they had measurable disease, a platelet count >75,000, an absolute neutrophil count >1,000, and a creatinine and bilirubin <2x laboratory upper limit of normal. Patients received RAD001 10 mg PO daily and were evaluated monthly. Dose reductions to 5 mg daily and 5 mg every other day were allowed. Response was assessed after 2 cycles and periodically thereafter. Patients could remain on drug until progression or toxicity. Results: Thirty-seven pts were treated - 20 (54%) with relapsed diffuse large cell (DLC), 14 (38%) with relapsed mantle cell (MCL), 2 high grade, and 1 follicular grade III. The median age was 72 years (range, 45–92). Patients had received a median of 4 prior therapies (range, 1–15). The overall response rate was 32% (12/37; 95% CI:20–49%) with 1 complete response and 11 partial responses. The ORR was 35% (7/20) in the DLC group and 29% (4/14) in the MCL patients. Patients have received a median of 2 cycles (range, 1–16+) of therapy. The median time to progression for all 37 patients is 3.1 months (95%CI; 2.0 – 4.7). The median duration of response for the 12 responders is 5.5 months (95% CI; 2.3 – 9.2) and 5 pts remained progression free at 6 months. Three patients are currently maintaining a response with a median time of 10.5 months (range, 2.9–15.6+months). RAD001 was well tolerated. The incidence of grade 3 anemia, neutropenia, and thrombocytopenia in this heavily pretreated pt population was 11%, 16%, and 30%. Two pts developed grade 4 neutropenia. Grade 2 hypercholesterolemia occurred in 11%; grade 2 hyperglycemia in 16%; grade 3 hyperglycemia in 11% and 1 pt had grade 4 hypertriglyceridemia. Summary: RAD001 has single-agent activity in relapsed aggressive NHL and provides proof-of-concept that targeting the mTOR pathway in NHL is clinically relevant.

Abstract Background: CpG 7909 is a synthetic 24 mer oligodeoxynucleotide designed to provide optimal activation of immune mechanisms through the TLR9 receptors on B-cells and plasmacytoid dendritic cells. In vitro CpG can upregulate CD20 expression as well as stimulate the immune system. Radioimmunotherapy (RIT) with anti-CD20 radioimmunoconjugates such as Zevalin produces responses in approximately 80% of patients with relapsed indolent lymphoma; however, only 30% obtain a complete response and 20% have long-term disease free survival. Objectives: To combine CpG 7909 with rituximab and Zevalin to enhance the response to RIT. Patients and Methods: Patients were eligible if they had biopsy proven relapsed, refractory, or residual CD20+ NHL. Disease types included relapsed indolent and aggressive B-cell NHL. Patients were required to have measurable disease, a platelet count >150,000, and an absolute neutrophil count >1,500. This was a phase I study where all patients received a standard dose of Zevalin (0.4mCi/kg with a maximum of 32mCi for patients over 80kg) along with a phase I dose of CpG 7909. Four dose levels were studied—0.08mg/kg; 0.16mg/kg; 0.32mg/kg; and 0.48mg/kg. CpG was dosed on Day 6, 13, 20, and 27; rituximab was provided Day 1, 8, and 15; indium-111 Zevalin on Day 1 and 8 (followed by indium-111 Zevalin imaging); and yttrium-90 Zevalin on Day 15. Response was assessed at week 4 and week 12. Patients are also being assayed pre- and post-CpG and at multiple time points up to 1 year following treatment for changes in T-cell, NK-cell, and cytokine levels. Results: A total of 30 patients have now been enrolled—6 at each of the first 3 dose levels and 12 at dose level 4. Three pts had relapsed diffuse large cell (DLC) and 27 pts were relapsed indolent. One of the first 6 patients at dose level 4 (0.48mg/kg) had a dose limiting toxicity (DLT - hematologic with full recovery). The other 5 patients at dose level 4 did not have DLT; and thus, 0.48mg/kg was determined to be the dose for further studies. An additional 6 patients at dose level 0.48mg/kg were accrued. Response information is available on the first 26 pts and the median follow-up is 12.4 months (range, 0–30.8). The overall response rate, to date, is 92% (24/26) – 66% (2/3) for the DLC pts and 96% (22/23) for the indolent pts. The complete remission rate is 58% (15/26). After follow-up, 7 of the 26 patients have progressed and one has died of relapsed NHL; therefore, 73% (19/26) remain in response and overall survival is 97% (29/30). As part of the study, we performed indium-111 Zevalin imaging before CpG and after 1 dose of CpG (prior to the yttrium-90 Zevalin) to evaluate the effect of CpG on the biodistribution of the radioimmunoconjugate. In the first 24 patients treated to date, review of the paired gamma camera images does not show any significant effects of CpG on tumor or normal organ biodistribution. To date, there has been no significant differences in T-cell, NK-cell, and cytokine activation by CpG dose level. Summary: CpG 7909 can be safely combined with Zevalin RIT in patients with advanced stage relapsed B-cell NHL.

Abstract Peripheral blood absolute lymphocyte count (ALC) at diagnosis is a predictor of survival in B-cell lymphomas. The role of ALC at diagnosis on survival in T-cell lymphoma has not been studied. Thus, we studied the role of ALC at diagnosis on clinical outcome in adult patients with primary anaplastic large cell lymphoma (PALCL) that were diagnosed, treated, and followed at the Mayo Clinic, Rochester. Between 1985 and 2006, 50 patients with PALCL qualified for the study. ALC was identified to be a strong predictor for complete response (CR), area under the curve (AUC = 0.83, p < 0.002). The median follow-up was 31.8 months (range: 1–212.6 months). ALC, as a continuous variable was a predictor for overall survival (OS) (HR = 0.143; 95%CI = 0.042–0.416; p < 0.0001) and progression-free survival (PFS) (HR = 0.150; 95%CI = 0.047–0.415; p < 0.0001) .Superior OS and PFS (Figure 1) were observed with an ALC ≥ 1.0 x 109/L (N = 31) versus an ALC < 1.0 x 109/L (N=19) (median OS: not reached vs 7.5 months, OS rates at 5 years, 81% vs 36%, p < 0.0006, respectively; and median PFS: not reached vs 6.3 months; PFS rates at 5 years, 77% vs 37%, p < 0.0007, respectively). Multivariate analysis demonstrated ALC to be an independent prognostic indicator for OS (HR = 0.196; 95%CI = 0.125–0.693; p < 0.002) and PFS (HR = 0.191; 95%CI = 0.053–0.559; p < 0.0008) when compared to anaplastic lymphoma kinase, international prognostic index, and cutaneous versus systemic presentation. Figure 1 Figure 1.

Abstract The interactions between leukemic cells and the bone marrow microenvironment play a critical role in angiogenesis, disease progression and cell adhesion mediated drug resistance (CAM-DR). VLA-4 (CD49d) is one of the most important adhesion receptors involved in these interactions. The binding of VLA-4 to fibronectin was shown to protect CLL B-cell from apoptosis (de la Fuente, 1999). The introduction of monoclonal antibodies targeting VLA-4 provides the opportunity for the development of novel treatment strategies. We examined the ability of VLA-4 blocking antibodies to induce apoptosis and overcome CAM-DR of primary B cells from CLL patients. Methods: Blood samples were obtained from consenting CLL patients. Mononuclear cells were isolated by density gradient centrifugation. Only samples with over 80% CLL B cells as assessed by flow cytometry (minimum 80% CD19+/CD5+ cells) were used. HS-5 human stromal cell line was cultured in 24 well plates (10% FCS DMEM media) and grown until they reached confluence. The confluent cells were then washed with PBS and incubated with AIM-V media 24 hours before CLL cells were co-cultured. CLL B cells were incubated in AIM-V media with and without fludarabine (1 mmol/L) for 24 hours, spun and resuspended in AIM-V. CLL B cells were then incubated with or without anti VLA-4 antibodies (BD Biosciences) at 10 μg/106 CLL cells for 2 hours and directly added into a co-culture with HS-5 cells. The CLL B cells remained in the co-culture for 24 hours, and were then collected and analyzed by flow cytometry for apoptosis/cell death by annexin/propidium iodide assay (i.e., total culture time 48 hours). Paired T-test was used to compare B cell viability results. Results: After 48 hour culture, the viability cells cultured in media alone or fludarabine for the first 24 hours were 40.6% (18.2%–73.7%) and 8.5% (0.2%–17.9%) respectively. Significant rescue from fludarabine induced cell death was seen if CLL B cells were co-cultured with HS-5 stromal cells for the second 24 hours rather than media alone (86.5% vs. 8.5%; p<0.001). The addition of anti VLA-4 antibodies, reduced stromal cell rescue from fludarabine induced apoptosis by 30% (61.5% vs. 86.5%; p= 0.0053). The addition of VLA-4 antibodies to untreated CLL B cells cultured with stromal cells had no effect on cell viability (90.2% vs. 91.2 p=0.59). Conclusion: Stromal cell adhesion rescues CLL B-cells from fludarabine induced apoptosis. Stromal cell rescue of CLL B-cells from drug induced apoptosis can be significantly reduced by blocking VLA-4 mediated cell adhesion of CLL B-cells to stromal cells. Blocking VLA-4 has no effect on the survival of untreated CLL B cells cultured with stromal cells suggesting the interaction mediated by VLA-4 protects against drug induced cell death rather than directly inducing apoptosis. These findings suggest anti VLA-4 antibodies are unlikely to be useful as a single agent therapy for treatment of CLL. However, blocking VLA-4 may enhance the efficacy of other agents used to treat CLL by overcoming adhesion mediated protection against drug induced cell death.