ASXL1 and DNMT3A mutation in a cytogenetically normal B3 thymoma.

The molecular drivers of thymoma are poorly understood. Outside of the identification of rarely occurring epidermal growth factor receptor and v-kit Hardy-Zuckerman 4 feline sarcoma viral oncogene homolog mutations via candidate gene sequencing, mutations in common cancer genes have yet to be observed. Only a single thymoma genome sequence has been previously reported, with no mutations in known cancer genes identified. Thus, we attempted to identify somatic driver mutations in a cytogenetically normal thymoma. A stage IVB type B3 thymoma from a 47-year-old male of Asian descent with no history of myasthenia gravis or other autoimmune condition was genomically evaluated. Exome sequencing and low-pass whole-genome sequencing was performed to identify somatic point mutations, copy number changes and structural variants. Mutations in known tumor suppressors DNMT3A (p.G728D) and ASXL1 (p.E657fs), consistent with mutations of known consequence in acute myeloid leukemia, were identified. Contrary to a previous report, this finding suggests the genetic etiology of thymomas may not be fundamentally distinct from other tumor types. Rather, these findings suggest that further sequencing of cytogenetically normal thymoma samples should reveal the specific molecular drivers of thymoma.

Expression of both B7-1 and CD28 contributes to the IL-2 responsiveness of CTLL-2 cells.

The CTLL-2 bioassay is used frequently to determine interleukin-2 (IL-2) concentrations in experimental samples, including samples that contain reagents which affect the CD28-B7 interaction. We therefore evaluated whether the CD28-B7 pathway plays a role in the growth of CTLL-2 cells. Flow cytometry demonstrated that CTLL-2 cells express both CD28 and B7-1. CTLA4-immunoglobulin (CTLA4-Ig) inhibited the growth of CTLL-2 cells over a range of IL-2 concentrations, suggesting that the CD28-B7 interaction plays an important role in the growth of CTLL-2 cells. Anti-B7-1 antibody also inhibited CTLL-2 proliferation at all concentrations of IL-2. These results indicate that the CTLL-2 bioassay may not be a reliable means of determining IL-2 levels in experimental samples containing reagents that affect the CD28-B7 interaction. They also suggest that co-expression of CD28 and B7 may contribute to the growth of malignant T cells.

T cell activation and cytokine production in anti-CD3 bispecific antibody therapy.

The 38C13 murine lymphoma model was used to examine the role T cell activation plays in anti-CD3-based bispecific antibody therapy by comparing two bispecific antibody preparations that vary in their ability to activate T cells. Prior studies demonstrated that lower dose bispecific IgG (BsIgG) induced nonspecific T cell activation in vitro and in vivo, whereas bispecific F(ab')2 [bsF(ab')2] did not. BsIgG was more effective than bsF(ab')2 at prolonging survival of tumor-bearing mice. BsF(ab')2 was effective at prolonging survival when used along with IL-2. When used at a lower dose, the antitumor effect of both preparations was specific in that it was limited to cells bearing the target antigen. In contrast, larger doses of bsIgG, but not bsF(ab')2, resulted in regression of antigen-negative tumor, and so had therapeutic effects that were nonspecific. Serum from mice treated with larger dose bsIgG contained IFN-gamma that inhibited the growth of tumor cells in vitro. We conclude that two distinct mechanisms of action are playing a role in the observed antitumor effects. BsF(ab')2 and lower dose bsIgG inhibit tumor growth by retargeting T cells. Higher dose bsIgG also results in nonspecific T cell activation and systemic cytokine production that induces tumor regression.

Chemotaxis in experimental syphilis.

Peritoneal exudate leukocytes from normal and Treponema pallidum-infected rabbits were examined for their chemotactic response to various chemoattractants and treponemal preparations. Leukocytes from normal and infected animals responded well to bacterial and serum-derived chemoattractants. Suspensions of washed Treponema phagedenis biotype Reiter but not T. pallidum exerted significant chemotactic activity. Cells from rabbits infected for greater than or equal to 7 days demonstrated increased locomotion, suggesting the possibility of increased random motility.