Superantigens related to B cell hyperplasia

CpG oligodeoxynucleotide-induced immunity prevents growth of germinal center-derived B lymphoma cells

Therapeutic efficacy of CpG oligodeoxynucleotide (ODN) ISS 1018 was tested in a murine B cell lymphoma model. Previous studies showed that the B lymphoma cells of SJL mice stimulate vigorous proliferation of host CD4(+) TH cells that is unaccompanied by development of tumor-specific CTL. In the presence of ISS 1018, however, tumor cells stimulated high levels of CTL activity in vitro, and this cytotoxic activity was inhibited when anti-IL-12 mAb was added to the cultures. Tumor cells pre-incubated with ISS 1018 were also able to generate CTL without addition of exogenous ODN, and FACS analysis revealed that following incubation with ISS 1018 for 24 h, tumor cells exhibited upregulation of MHC I, MHC II, and co-stimulatory molecule CD80. Finally, tumor-injected mice treated with ISS 1018 showed significantly less growth of tumor cells in lymph nodes and spleen, and exhibited prolonged survival compared to mice treated with a control ODN. The documented effects of CpG ODNs to stimulate cytokines, such as IL-12, from antigen presenting cells, and to upregulate expression of MHC Class I and Class II, as well as co-stimulatory molecules on tumor cells, are also the likely mechanisms by which CTL are generated by ISS 1018 in the SJL B cell lymphoma model.

Tim-3+ T-bet+ tumor-specific Th1 cells colocalize with and inhibit development and growth of murine neoplasms

Although T cells infiltrate many types of murine and human neoplasms, in many instances tumor-specific cytotoxicity is not observed. Strategies to stimulate CTL-mediated antitumor immunity have included in vitro stimulation and/or genetic engineering of T cells, followed by adoptive transfer into tumor-bearing hosts. In this model of B cell lymphoma in SJL/J mice, we used Tim-3(+) T-bet(+) Th1 cells to facilitate the development of tumor-specific CTL. Tumor-specific Th1 cell lines were polarized with IL-12 during in vitro stimulation and long term maintenance. As few as 5 million Tim-3(+) T-bet(+) Th1 cells enabled recipients to resist growth of malignant transplantable cells. In addition, similar numbers of Th1 cells injected into 2- to 3-mo-old mice inhibited development of the spontaneous primary lymphomas, which normally arise in 90% of aging mice. CFSE(+) Th1 cells colocalized with injected tumor cells in vivo and formed conjugates with the tumor cells within follicles, whereas in nontumor-challenged recipients the CFSE(+) Th1 cells localized only within the T cell zones of the spleen. These results provide evidence that adoptive immunotherapy with Tim-3(+) T-bet(+) tumor-specific Th1 cells can be used to induce host cytotoxic responses that inhibit the development and growth of neoplastic cells.

Interleukin-12-induced cytotoxicity against syngeneic B cell lymphomas of SJL/J mice

The B cell lymphomas (RCS) that develop spontaneously in 90% of aging SJL/J mice stimulate syngeneic CD4+ Vbeta16+ Th2 cells to produce cytokines, such as IL-4 and IL-5, which promote lymphoma growth. Although RCS cells express a unique superantigen (vSAg) encoded by an endogenous MMTV (Mtv-29) provirus that also elicits IFN-gamma production from naïve syngeneic lymphoid cells, there is no development of RCS-specific cytotoxicity. However, addition of IL-12 to co-cultures of SJL spleen and irradiated (gamma-)RCS cells resulted in the appearance of effector cells that killed RCS and NK-susceptible target cells. Antibody depletion studies revealed at least two types of RCS/IL-12-induced cytotoxic cells: (1) NK cells (Asialo GM1+) and (2) CD8+ CTL. Despite high titers of IFN-gamma in the SN of co-culture of SJL spleen and gamma-RCS cells, cytotoxicity only developed if IL-12 was also included in the co-cultures. The results of RNAse protection assays and multi-parameter FACS analysis demonstrated an upregulation of IFN-gamma and decrease in IL-4 by activated Th cells in co-cultures with IL-12. These results indicate that inclusion of IL-12 in primary co-cultures of SJL spleen and gamma-RCS cells influences the qualitative nature of the response to favor use of RCS-responsive Th1 rather than Th2 cells to facilitate the production of cytotoxic effector cells. Results of in vivo experiments support this hypothesis, as judged by tumor growth assays and FACS analysis of the tumor cell content of lymphoid tissues. Inhibition of lymphoma growth was observed in mice given gamma-RCS/IL-12-induced effector cells prior to injection of viable RCS cells. These results demonstrate that IL-12 can be used to alter the host immune response leading to induction of cytotoxic effector cells that inhibit the development and/or progressive growth of otherwise resistant B cell lymphomas in SJL/J mice.

Requirement for reverse immune surveillance for the growth of germinal center-derived murine lymphomas

The concept of reverse immune surveillance, first conceived over 12 years ago, described the relationship that existed between germinal center-derived B cell lymphoma cells and the host immune system in SjL/J mice. According to reverse immune surveillance, recognition of tumor cell antigens and a response by the host immune system is required for tumor growth. The phenomenon of reverse immune surveillance related to B cell lymphomas has recently also been characterized in another inbred mouse strain, C57L/J. Moreover, elements of reverse immune surveillance have been observed in several other mouse strains that develop B cell lymphomas, suggesting that this lymphomagenic mechanism may be more common than first envisioned. In SJL and C57L mice, the B lymphoma cells express an MMTV-encoded superantigen (vSAg29) that stimulates syngeneic CD4+ T cells bearing Vbeta16 in their TCR. In contrast to the mRNAs for other MMTVs in normal mouse B cells, vSAg29 mRNA initiates in the env (META) region, undergoes splicing in the 3' env region, and continues through the 3' LTR. Copious cytokine production, including IFN-gamma, IL-4 and IL-5 accompanies the response of the T cells to this vSAg. In addition to cytokines produced by vSAg-responsive T cells, more recent evidence indicates that another cytokine, LTalphabeta2, which is expressed on the lymphoma cell surface, also plays a role in the promotion of the B cell lymphoma growth. It is possible that interaction with LTbeta-R on follicular dendritic cells or other stromal elements facilitates tumor growth by preventing apoptosis of the malignant B cells. To what degree these findings in the mouse are relevant to the development and/or growth of human B lymphoma cells remains to be determined. However, endogenous retroviral sequences do exist in the human genome. Interestingly, some of these sequences are homologous to MMTV, and are transcribed in B lymphoblastoid cells. Moreover microorganisms that are infectious for human B cells, such as EBV and Herpes Virus 8, may also produce superantigens.

B cell lymphomas of C57L/J mice; the role of natural killer cells and T helper cells in lymphoma development and growth

The Hodgkin's-like Type B neoplasms which arise spontaneously in aging C57L mice (25% incidence at 21 months of age) were first reported over 40 years ago, but since then relatively little has been published about these lymphomas. Based on previous studies in SJL mice, we investigated the phenotypic and functional properties of C57L-derived lymphomas in relation to Mtv29-encoded vSAg expression by the tumor cells, and their ability to stimulate TCR Vbeta-restricted T cells. The cell surface phenotype of the C57L lymphomas indicates a B cell origin (sIg(+), MHC II(+)). These B lymphoma cells also express co-stimulatory molecules [B7-1 (CD80) and HSA (CD24)], and stimulate marked proliferation of syngeneic CD4(+) T cells. C57L B lymphoma cells exhibit Mtv-encoded mRNA by northern analysis, and also stimulate IL-2 production from Vbeta16(+) T cell hybrids, suggesting a role for Mtv 29 in this syngeneic T cell response. After transfer to syngeneic recipients, primary C57L lymphomas grow slowly, if at all. However, tumor growth is greatly accelerated by pretreatment of C57L recipients with anti-asialo GM1 antibody (but not anti-CD8 mAb), suggesting that NK cells play a major role in inhibiting lymphoma growth. If, in addition to anti-asialo GM1, the mice are also pretreated with anti-CD4 mAb, tumor growth is markedly inhibited, indicating that the lymphoma-responsive syngeneic CD4(+) T cells promote tumor growth. Therefore, although the vSAg-induced response stimulated by vSAg29 expressing lymphoma cells in syngeneic TCR Vbeta-restricted CD4(+) T cells is an important etiologic factor in this type of B cell neoplasm both in C57L and in SJL mice, the final outcome of the spontaneous neoplastic process appears strongly influenced by endogenous NK activity in aging mice.