HLA-G engineering reprograms CAR-T cells with an immune privilege

Abstract

Personalized T cell therapy empowered by chimeric antigen receptor (CAR) that recognizes specific tumor antigen has cured numerous blood cancer patients since its initial approval in 2017. However, its access to a broader population has been limited by the unavailability of an off-the-shelf product derived from an allogeneic donor that can evade immune rejection, which is mediated by polymorphic class I and class II human leukocyte antigens (HLAs). Since class II HLAs are only expressed in specialized antigen-presenting cells but not T cells, it might suffice to evade T cells by deleting the common class I HLA light chain Beta-2 Microglobulin (B2M) (1). However, B2M-deficient cells can trigger a "missing-self" response to activate natural killer (NK) cells (2), a second function that was evolved to compensate loss of T cell response. Inserting a less polymorphic class I HLA gene encoding a known NK inhibitory ligand, namely HLA-E or HLA-G (3), into the B2M locus so that the endogenous B2M expression is disrupted could theoretically allow evasion of both T and NK cells. Despite being a seemingly better candidate in that HLA-G is uniquely expressed in immune-privileged sites such as the placenta with a believed function in protecting the fetus from immune rejection by the pregnant mother, whereas ubiquitously-expressing HLA-E is known to bind both inhibitory and activating NK receptors (4, 5), only HLA-E engineering has been attempted yet without convincing success in vivo (6, 7). Here, we generate an off-the-shelf CAR-T product with B2M replaced by a gene fusion encoding an HLA-G single-chain trimer under minimally impacted B2M epigenetic landscape, and observe its immune evasion property and a tumor-inhibitory function that is equivalent to its autologous control using a humanized mouse model for the first time with T and NK cells reconstituted from a donor with a distant HLA haplotype. HLA-G engineering may thus reprogram T cells into an immune-privileged state that can be utilized for all cell-based therapies.