Genetic analysis of the Mls system. Formal Mls typing of the commonly used inbred strains

Uncoupling therapeutic from immunotherapy-related adverse effects for safer and effective anti-CTLA-4 antibodies in CTLA4 humanized mice

Anti-CTLA-4 monoclonal antibodies (mAbs) confer a cancer immunotherapeutic effect (CITE) but cause severe immunotherapy-related adverse events (irAE). Targeting CTLA-4 has shown remarkable long-term benefit and thus remains a valuable tool for cancer immunotherapy if the irAE can be brought under control. An animal model, which recapitulates clinical irAE and CITE, would be valuable for developing safer CTLA-4-targeting reagents. Here, we report such a model using mice harboring the humanized Ctla4 gene. In this model, the clinically used drug, Ipilimumab, induced severe irAE especially when combined with an anti-PD-1 antibody; whereas another mAb, L3D10, induced comparable CITE with very mild irAE under the same conditions. The irAE corresponded to systemic T cell activation and resulted in reduced ratios of regulatory to effector T cells (Treg/Teff) among autoreactive T cells. Using mice that were either homozygous or heterozygous for the human allele, we found that the irAE required bi-allelic engagement, while CITE only required monoallelic engagement. As with the immunological distinction for monoallelic vs bi-allelic engagement, we found that bi-allelic engagement of the Ctla4 gene was necessary for preventing conversion of autoreactive T cells into Treg cells. Humanization of L3D10, which led to loss of blocking activity, further increased safety without affecting the therapeutic effect. Taken together, our data demonstrate that complete CTLA-4 occupation, systemic T cell activation and preferential expansion of self-reactive T cells are dispensable for tumor rejection but correlate with irAE, while blocking B7-CTLA-4 interaction impacts neither safety nor efficacy of anti-CTLA-4 antibodies. These data provide important insights for the clinical development of safer and potentially more effective CTLA-4-targeting immunotherapy.

Selective elimination of autoreactive T cells in vivo by the regulatory T cells

How regulatory T cells (Treg) control autoreactive T cells has not been analyzed in animals with a normal T cell repertoire. Using endogenous viral superantigens (VSAg) as the primary self antigens and mice with the Scurfy mutation of FoxP3, we show here that the Treg defect causes preferential accumulation of autoreactive T cells. Interestingly, in the Scurfy mice, the proliferation of VSAg-reactive T cells was no more vigorous than that of non-VSAg-reactive T cells, which indicated that the preferential accumulation is not due to preferential proliferation. In contrast, VSAg-reactive T cells disappears in WT host despite their preferential proliferation. Importantly, when adoptively transferred into the newborn Scurfy mice, the Treg selectively kill autoreactive T cells without affecting their proliferation. The selective elimination is due to increased susceptibility of autoreactive T cells to Treg-mediated killing.

Perinatal blockade of b7-1 and b7-2 inhibits clonal deletion of highly pathogenic autoreactive T cells

A number of in vitro studies have suggested that costimulatory molecules B7-1 and B7-2 and their receptor CD28 can promote clonal deletion, and limited in vivo studies have indicated that CD28 is involved in the clonal deletion of some T cells. However, the significance of B7-mediated clonal deletion in preventing autoimmune diseases has not been studied systematically. Here we report that the perinatal blockade of B7-1 and B7-2 substantially inhibits the clonal deletion of T cells in the thymus and leads to an accumulation of T cells capable of inducing fatal multiorgan inflammation. These results reveal a critical role for costimulatory molecules B7-1 and B7-2 in deleting pathogenic autoreactive T cells in the thymus. The critical role of B7-1 and B7-2 in T cell clonal deletion may explain, at least in part, the paradoxical increase of autoimmune disease in mice deficient for this family of costimulatory molecules, such as cytotoxic T lymphocyte associated molecule 4, CD28, and B7-2. The strong pathogenicity of the self-reactive T cells supports a central hypothesis in immunology, which is that clonal deletion plays an important role in preventing autoimmune diseases.

Oligoclonal expansion of T cell receptor V beta 2 and 3 cells in the livers of mice with graft-versus-host disease

The nonsuppurrative destructive cholangitis lesions in the B10.D2 (donor) into BALB/c (host) mouse graft-versus-host disease (GVHD) model are dependent on CD4 T cells that use a T cell receptor-beta chain variable region (Vbeta) repertoire, which is heavily biased toward Vbeta2 and Vbeta3 usage. We hypothesized that liver Vbeta2(+) and Vbeta3(+) CD4 T cells originate from donor mice and recognize BALB/c minor histocompatibility alloantigens and BALB/c endogenous retroviral superantigen-6, respectively. To test this hypothesis, we determined the donor:host chimera status of infiltrating liver lymphocytes and the clonal states of liver Vbeta2(+) and liver Vbeta3(+) CD4 cells isolated from GVHD mice. A limited donor TCR Vbeta repertoire composed of Vbeta1(+), 2(+), 3(+), 4(+), 6(+), and 8(+) cells infiltrated the livers of GVHD mice on day 3. Consistent with a response to immunodominant host minor histocompatibility antigens, we detected oligoclonal liver Vbeta2(+) T cells in 40% of GVHD mice studied on day 3 and in 100% of GVHD mice studied on day 14. Typical of superantigen stimulation, extremely polyclonal liver Vbeta3(+) T cells were detected in 100% of GVHD mice studied on day 3 and 40% of GVHD mice studied on day 14. Yet, the liver Vbeta3(+) T cells in 60% of the day 14 GVHD mice were oligoclonal, pointing to a response to minor histocompatibility antigens.

T cell repertoire expression in murine recipients of bone marrow transplant after LF 08-0299 (Tresperimus) administration

LF 08-0299 (Tresperimus), a novel immunosuppressive compound, has been previously shown to prevent graft-versus-host disease in murine models. In this study, we investigated the influence of LF 08-0299 on the TCR Vbeta repertoire of irradiated F1 recipient mice reconstituted with either syngeneic or parental bone marrow cells. We showed that a partial blockade of thymic differentiation occurred in normal mice under treatment at the transition CD4-/CD8- to CD4+/CD8+, and that this blockade was fully reversible. Despite the effect on the thymus, normal T cell repertoire negative selection was preserved following syngeneic bone marrow transplantation. We further assessed whether LF 08-0299 administration could modify Vbeta T cell expression in irradiated recipients reconstituted with parental bone marrow cells. In our murine parental to F1 transplant model, abnormal TCR Vbeta3, Vbeta5, Vbeta6 and Vbeta11 expression was demonstrated in peripheral lymph nodes of irradiated recipients. Moreover, Vbeta6 and Vbeta3 T cell populations were overexpressed. Administration of LF 08-0299 modified the pattern of Vbeta T cell expression. The expansion of Vbeta6 T cells was selectively inhibited under LF 08-0299 therapy and, in contrast, Vbeta5 T cells were overexpressed. Lymph node histological analysis showed that LF 08-0299 administration fully prevented the graft-versus-host reaction occurring in untreated recipient mice.

Influence of graft versus host reaction on the T cell repertoire differentiating from bone marrow precursors following allogeneic bone marrow transplantation

When lethally irradiated AKR (Mls-1a) mice were reconstituted with bone marrow (BM) cells plus a small number (0.5%) of mature T cells from allogeneic B10.AQR or B10 (Mls-1b) mice and minor GVHR was induced in the recipients, almost complete donor chimerism was accomplished in the early stages after reconstitution. By contrast, in irradiated AKR mice reconstituted with T cell-depleted BM cells alone from B10 or B10.AQR mice, radio-resistant T cells of recipient origin persisted for a relatively long period in peripheral lymphoid tissues. In this paper the influence of residual T cells in the chimeric mice on generation of the T cell repertoire derived from donor BM is discussed. It will be demonstrated that the recipient (AKR) T cells are capable of producing Mls-1a antigens (Ag) after lethal irradiation in vivo. These recipient T cells eventually induce clonal elimination of Mls-1a reactive V beta 6+, V beta 8.1+ and V beta 9+ T cells derived from developing thymocytes of donor BM origin. The Mls-1a reactive T cells are not eliminated in GVHR chimeras in which recipient T cells are absent. However, V beta 5+ T cells reactive to I-E plus Etc-1 Ag are deleted in the chimeras undergoing GVHR. These results indicate that recipient cells which produce tissue-specific antigens (tolerogens) should be taken into consideration when generation of the T cell repertoire of donor origin following allogeneic BM transplantation is investigated.

Superantigens and their potential role in human disease

In the past few years, there has been a virtual explosion of information on the viral and bacterial molecules now known as superantigens. Some structures have been defined and the mechanism by which they interact with MHC class II and the V beta region of the T cell receptor is being clarified. Data are accumulating regarding the importance of virally encoded superantigens in infectivity, viral replication, and the life cycle of the virus. In the case of MMTV, evidence also suggests that superantigens encoded by a provirus may be maintained by the host to protect against future exogenous MMTV infection. Experiments in animals have also begun to elucidate the dramatic and variable effects of superantigens on responding T cells and other immune processes. Finally, the role of superantigens in certain human diseases such as toxic shock syndrome, some autoimmune diseases like Kawasaki syndrome, and perhaps some immunodeficiency disease such as that secondary to HIV infection is being addressed and mechanisms are being defined. Still, numerous important questions remain. For example, it is not clear how superantigens with such different structures, for example, SEB, TSST-1, and MMTV vSAG, can interact with MHC and a similar region of the TCR in such basically similar ways. It remains to be determined whether there are human equivalents of the endogenous murine MMTV superantigens. The functional role of bacterial superantigens also remains to be explained. Serious infection and serious consequences from toxin-producing bacteria are relatively rare events, and it is questionable whether such events are involved in the selection pressure to maintain production of a functional superantigen. Hypotheses to explain these molecules, which can differ greatly in structure, include T cell stimulation-mediated suppression of host responses or enhancement of environments for bacterial growth and replication, but substantiating data for these ideas are mostly absent. It also seems likely that only the tip of the iceberg has been uncovered in terms of the role of superantigens in human disease. Unlike toxic shock syndrome, other associations, especially with viral superantigens, may be quite subtle and defined only after considerable effort. The definition of these molecules and mechanisms of disease may result in new therapeutic strategies. Finally, it is apparent that superantigens have dramatic effects on the immune system. One wonders whether these molecules or modifications of them can be used as specific modulators of the immune system to treat disease.

Acquired Mls-1a-like clonal deletion in Mls-1b mice

BALB/c mice (H-2d, Mls-1b) from one colony progressively modify their T cell repertoire during aging, by deleting T cells that express products of the V beta 6 and V beta 8.1 genes of the T cell receptor. Clonal deletion occurs only in 50% of mice between 27 and 43 wk of age, affecting thymus, spleen, and lymph node T cells. The phenomenon is progressive and seems to affect nearly all thymuses between 14 and 19 wk of age. CD4+CD8- mature T cells are more affected than CD4-CD8+ cells. In the thymus, deletion occurs at the stage of immature J11d+ cells expressing a high level of V beta 6, while J11d+V beta 6low- expressing cells are not modified. Clonal deletion is thus an early phenomenon that deletes cells of the immature generative compartment in the thymus. This Mls-1a-like clonal deletion is associated neither with the expression of an Mls-1a-like antigen that could be identified in mixed lymphocyte reaction in vitro, nor with the presence of Mtv-7, the endogenous mouse mammary tumor virus (MMTV) proviral loci. Spleen cells, bone marrow cells, and total thymocytes injected into newborn thymuses cannot induce V beta 6+ cell deletion. However, newborn thymuses grafted into old BALB/c mice behave like their recipients, suggesting that a new antigen, present in these old BALB/c mice, is indeed able to induce an Mls-1a-like clonal deletion. As other BALB/c colonies tested do not behave in same way, the hypothesis of a new exogenous deleting factor rather than a genetic transmission is likely. This may suggest that acquired clonal deletion is a more common phenomenon than expected, and may be the spontaneous reaction of the immune system to the introduction of a new retrovirus or other superantigen.

The open reading frames in the 3' long terminal repeats of several mouse mammary tumor virus integrants encode V beta 3-specific superantigens

Mice expressing the minor lymphocyte stimulation antigens, Mls-1a, -2a, or -3a, singly on the B10.BR background have been generated. Mls phenotypes correlate with the integration of mouse mammary tumor viruses (MTV) in the mouse genome. The open reading frames within the 3' long terminal repeats of the integrated MTVs 1, 3, 6, and 13 encode V beta 3-specific superantigens. Sequence data for these viral superantigens is presented, indicating that it is the COOH-terminal portion of the viral superantigen that interacts with the T cell receptor V beta element.