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

Abstract

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.

Sensitizing the Tumor Microenvironment to Immune Checkpoint Therapy

“…T-regs express high levels of CTLA4, and antibodies blocking CTLA4 can deplete T-regs in the TME in murine models, dependent on Fc subclass and host Fc receptor (42)(43)(44). T-reg depletion has also been hypothesized as a key mechanism of action for anti-CTLA4 treatment in humans (45,46), however clinical data does not support this (47), which may be due to the different isotype and Fc portion of the human antibody. Indeed, there is an association between pre-treatment Foxp3+ T-reg infiltration, followed by a subsequent increase in TILs 3 weeks into treatment in melanoma biopsies which was associated with response to the CTLA4-targeting antibody ipilimumab (48).…”

Hijacking antibody-induced CTLA-4 lysosomal degradation for safer and more effective cancer immunotherapy

“…29 In contrast, studies from several laboratories, including ours, established that selective depletion of regulatory T cells in the tumor microenvironment (TME) but not in the normal tissues as the primary mechanism of action of CITE. [29][30][31][32][33] The new understanding of regulatory T cell depletion explained why it is possible to uncouple irAE from CITE. 33,34 Unlike most cell-surface molecules, CTLA-4 recycles between the cell surface and endosomes, 35 where it is prevented from lysosomal degradation and recycles back to the cell surface by binding to the lipopolysaccharide-responsive and beige-like anchor (LRBA) protein.…”

“…[29][30][31][32][33] The new understanding of regulatory T cell depletion explained why it is possible to uncouple irAE from CITE. 33,34 Unlike most cell-surface molecules, CTLA-4 recycles between the cell surface and endosomes, 35 where it is prevented from lysosomal degradation and recycles back to the cell surface by binding to the lipopolysaccharide-responsive and beige-like anchor (LRBA) protein. 8,36 Since genetic mutations in either CTLA-4 5,8 or LRBA 8,36 cause autoimmune diseases in human, we hypothesize that anti-CTLA-4-induced irAE may relate to antibody-mediated disruption of CTLA-4 recycling.…”

An adapted anti-CTLA4 therapeutic aimed at mitigating the toxicities of checkpoint inhibition

“…Other groups have utilized human CTLA4 knockin models to interrogate irAE development in response to anti-CTLA4, anti-PD-1, or combination treatment (15). The examination of anti-CTLA4 DVD in the human CTLA4 mouse model would have strengthened the conclusions of Pai et al In addition, results from published studies regarding the effect of anti-CTLA4 therapy on Tregs in human tumors are varied, with some data suggesting these agents may not deplete Tregs (16), but may in fact expand the Treg pool (17) or even modulate Treg-suppressive function without actually affecting numbers (18).…”