Abstract 1992: Evaluating in vivo efficacy of peptide vaccines in humanized B-HLA-A2.1 mice
Authors: Yao Jiawei , Shang Chengzhang , Madaan Shivam , Nie Yanhui , Yang Yi 
Published: June 2022

Abstract
HLA-A molecules are αβ heterodimers that belong to the human leukocyte antigen (HLA) class I major histocompatibility complex (MHC) in humans. Class I molecules play a central role in the immune system by presenting intracellular peptides derived from the endoplasmic reticulum lumen, enabling recognition by cytotoxic T cells. The heavy α chain structure of HLA-A, encoded by the HLA-A gene, contains the leader peptide, the α1 and α2 domains that both bind the peptide, and the α3 domain that binds CD8 molecules, the transmembrane region, and the cytoplasmic tail. Polymorphisms within α1 and α2 domains of the heavy chain are responsible for the peptide binding specificity of each class I molecule, while the light β2-microglobulin (B2M) chain encoded by the B2M gene, is not known to be polymorphic. Among more than 6,000 HLA-A alleles, HLA-A2.1 is the most commonly expressed, and its peptide-binding motif is well understood. We developed MHC I humanized mice (B-HLA-A2.1 mice) expressing human HLA molecules to establish an in vivo experimental model for evaluating human HLA restricted T cell-mediated vaccine efficacy in oncology applications. Our strategy was to replace the B2m gene of the mouse with the sequences encompassing the human B2M CDS and HLA-A2.1 gene that included leader sequence, α1 and α2 domains ligated to a fragment of the mouse H-2Db gene encoding the α3, transmembrane and cytoplasmic domains. Using flow cytometry analysis, human B2M and HLA-A2.1 were detected in splenocytes of homozygous B-HLA-A2.1 mice but not in wild type mice. Mouse B2M was detectable in splenocytes of wild type mice but not in homozygous B-HLA-A2.1 mice. The percentage of T cells, B cells, CD4+ T cells, and CD8+ T cells within the spleens of homozygous B-HLA-A2.1 mice were similar to those in the wild type mice, demonstrating that introduction of human B2M and HLA-A2.1 does not change the overall development, differentiation, or distribution of these cell types. Next, in vivo efficacy evaluation of two peptide vaccines (V1 and V2) under development was performed with the humanized mice. Mice were inoculated with vaccines by intramuscular injections into the inner thigh (L and R) muscles and sacrificed three weeks after the last immunization. The splenocytes were extracted, stimulated with individual peptides, and measured for IFN-γ secretion. HLA-A2.1-restricted CTL responses of the vaccines were successfully detected in B-HLA-A2.1 mice, and no significant difference in body weight was observed among groups. Our results show that B-HLA-2.1 mice provide a powerful preclinical mouse model for in vivo evaluation of peptide vaccines.
Citation Format: Jiawei Yao, Chengzhang Shang, Shivam Madaan, Yanhui Nie, Yi Yang. Evaluating in vivo efficacy of peptide vaccines in humanized B-HLA-A2.1 mice [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 1992.