Background Chimeric antigen receptor (CAR) T cell adoptive therapies have proven efficacy in the treatment of hematological malignancies. However, there are challenges to the current CAR T cell manufacturing process, one being manufacturing failure due to dysfunctional, patient-derived T cells.¹ A proposed solution to overcoming this limitation is the development of universal CAR T (UCART) cells engineered from healthy, normal donor-derived T cells. Histocompatibility barriers must be addressed when creating the UCART cell. Ablation of the alpha/beta T cell receptor surface expression will prevent graft-versus-host disease while host-versus-graft responses will be mitigated by ablating the surface expression of the major histocompatibility complex (MHC) class I and II molecules.^2,3 These triple knockout (TKO) T cells could serve as universal recipients for development of the UCART cell. Importantly, a consequence of MHC class I ablation is NK cell activation due to the “missing-self” response.⁴ HLA-E, a non-classical MHC class I molecule, is known to interact with the NK cell inhibitory receptor NKG2A and we propose its overexpression on UCART cells will mitigate NK cell activation.

Methods Because the HLA-E/NKG2A interaction is dependent upon the peptide presented by HLA-E, 10 HLA-E single-chain trimer (SCT) constructs expressing various peptide sequences were created to determine which HLA-E/peptide complex would result in significant NK cell inhibition.⁵ K562 cells transduced to express these HLA-E/peptide complexes were used as a model for UCART cells in preliminary experiments.

Results An HLA-E SCT presenting an HLA-C leader peptide (HLA-E/C) resulted in significant inhibition of NK cells as determined by flow cytometry-based NK cell degranulation (CD107a) assays. Decreased lysis of K562 HLA-E/C -expressing target cells in ⁵¹Cr release assays further validated the inhibitory effect of HLA-E/C complexes on NK cell activation. Finally, HLA-E/C complex expression on TKO T cells lead to protection against NK lytic activity.

Conclusions Altogether these data demonstrate the effectiveness of selected HLA-E/peptide complexes to inhibit NK cell activation due to the “missing-self” response. Modifications such as the one described here may prevent UCART cell clearance due to host recognition (NK cell activation) and may ultimately lead to a more potent, safe, and long-term persistent UCART cell therapy.

References

1. Thommen DS, Schumacher TN. T cell dysfunction in cancer. Cancer Cell. 2018; 33:547–562.

2. Abdelhakim H, Abdel-Azim H, Saad A. Role of aß T cell depletion in prevention of graft versus host disease. Biomedicines. 2017; 5:35.

3. Wang D, Quan Y, Yan Q, Morales J. E, Wetsel RA. Targeted disruption of the ß2-microglobulin gene minimizes the immunogenicity of human embryonic stem cells. Stem Cells Transl Med. 2015; 4:1234–1245.

4. Ljunggren HG, Kärre K. In search of the ‘missing self’: MHC molecules and NK cell recognition. Immunol Today. 1990; 11:237–244.

5. Borrego F, Ulbrecht M, Weiss EH, Coligan JE, Brooks AG, Recognition of human histocompatibility leukocyte antigen (HLA)-E complexed with HLA class I signal sequence-derived peptides by CD94/NKG2 confers protection from natural killer cell-mediated lysis. J Exp Med 1998; 187:813–818.