Morse, Herbert C.

Abstract Systemic lupus erythematosus (SLE) inflicts damage via autoantibody complexes that result in multiorgan damage and renal failure. The BXSB.Yaa mouse is a well-established model of SLE. We show that genetic disruption of multiple components of the MHC I axis greatly accelerates autoimmune disease in this model. Mice lacking both CD8 and IL15 succumb to SLE-like disease earliest (mean age 14 wks), implying a protective role for CD8 T cells and potentially natural killer cells dependent on IL15. BXSB.Yaa mice develop an expanded population of CD8 T cells with increased expression of both CD122 and IL15Rα, which we propose is due to increased expression of IL15R on these cells. Neither Foxp3 nor CD25 are elevated, and IL10 deficient BXSB.Yaa mice fail to show accelerated disease. However, lytic function appears significant as BXSB.Yaa mice deficient in perforin show decreased survival. TCR analysis failed to suggest a biased CD8 T cell repertoire, suggesting that the cellular targets of suppression are not antigenically discrete. Overall, the results suggest the existence of potent MHC I-dependent suppressor cell population(s) that normally protect BXSB.Yaa mice from an even more aggressive form of SLE-like disease. Moreover, the results support a model in which suppression is unlikely to be mediated by cytokine regulation but instead by lytic mechanisms. Harnessing this inherent regulatory cell population could provide a novel strategy to treat SLE and related syndromes.

Abstract The time in cellular differentiation at which the expression of an oncogene is dysregulated is thought to determine the phenotype of the resulting neoplasia. We tested this assumption in C57BL6/J transgenic mice expressing an HA-tagged c-myc oncogene in B cells under the control of kappa light chain regulatory elements. Two transgenes were engineered that differed by only one nucleotide. The first set of mice carries a wild type HA-MYC transgene, develops pro-B cell tumors, and succumbs rapidly to pronounced lymphosplenomegaly. In the second set of mice, a point mutation in the HA-tag portion of the transgene creates a stop codon that abrogates HA-MYC translation. This stop codon was engineered to be a hotspot for somatic hypermutation. Thus sporadically, in a germinal center B cell, somatic hypermutation may revert the stop codon, allowing translation of HA-MYC. In two independently derived lines, mice spontaneously develop monoclonal gammopathies (50% incidence at 30 weeks (n=35), 80% at 40 weeks (n=35)). Serum protein electrophoresis detects M-spikes that increase in intensity over time, and 6 out of 7 cases tested so far were of IgG1 isotype. Unlike other mouse models of plasma cell neoplasia, no lymphosplenomegaly nor ascites were detected. In analogy to human multiple myeloma, that is a disease of isotype-switched and hypermutated cells homing to the bone, large populations of plasma cells were found in the bone marrow. Bone marrow (but not spleen) lysates reacted for HA and human MYC proteins by western blot and immunohistochemistry, thus indicating that reversion of the stop codon occurred. Remarkably, in two young mice, monoclonal spikes appeared 2 weeks after vaccination with NP-CGG. These spikes were sustained and the monoclonal protein was reactive to the NP antigen. Together, comparison of the two sets of mice demonstrates that activation of the same transgene at distinct B cell developmental stages results in dramatically different tumor phenotypes. In addition, and opposite to most engineered mice, we have created a system where the oncogene is turned on sporadically, as occurs in the human disease. Furthermore, we have developed a model that faithfully reproduces important clinical aspects of monoclonal gammopathy of undetermined significance (MGUS) and its progression to multiple myeloma. This model will be useful to develop immunologic and chemoterapeutic approaches.