Abstract
Human tumor xenograft models do not replicate the human immune system and tumor microenvironment. We developed an improved humanized mouse model, derived from fresh cord blood CD34(+) stem cells (CD34(+) HSC), and combined it with lung cancer cell line-derived human xenografts or patient-derived xenografts (Hu-PDX). Fresh CD34(+) HSCs could reconstitute detectable mature human leukocytes (hCD45(+)) in mice at four weeks without the onset of graft-versus-host disease (GVHD). Repopulated human T cells, B cells, natural killer (NK) cells, dendritic cells (DC), and myeloid-derived suppressor cells (MDSC) increased in peripheral blood, spleen, and bone marrow over time. Although cultured CD34(+) HSCs labeled with luciferase could be detected in mice, the cultured HSCs did not develop into mature human immune cells by four weeks, unlike fresh CD34(+) HSCs. Ex vivo, reconstituted T cells, obtained from the tumor-bearing humanized mice, secreted IFNγ upon treatment with phorbol myristate acetate (PMA) or exposure to human A549 lung tumor cells and mediated antigen-specific CTL responses, indicating functional activity. Growth of engrafted PDXs and tumor xenografts was not dependent on the human leukocyte antigen status of the donor. Treatment with the anti-PD-1 checkpoint inhibitors pembrolizumab or nivolumab inhibited tumor growth in humanized mice significantly, and correlated with an increased number of CTLs and decreased MDSCs, regardless of the donor HLA type. In conclusion, fresh CD34(+)HSCs are more effective than their expanded counterparts in humanizing mice, and do so in a shorter time. The Hu-PDX model provides an improved platform for evaluation of immunotherapy.