877 Assessment of γδ T cell therapies in humanized mice

<h3>Background</h3> Current therapeutic approaches involving gd T cell include adoptive cell transfer, in vivo stimulation and combined therapies. While preliminary results are promising, investigation of such therapies in preclinical models is challenging, because γδ T cells are not developed at satisfactory levels in most of the humanized mouse models. <h3>Methods</h3> Here we described the presence and functionality of γδ T cell in BRGSF (Balb/C Rag2^-/-, IL2Rγ^-/-, SIRPαNOD and Flt3^-/-), a highly immunodeficient mouse featuring reduced murine myeloid cells. BRGSF mice reconstituted with human cord blood CD34⁺ cells (BRGSF-HIS) develop functional lymphoid and myeloid compartments. This engraftment is stable for over a year¹ and mice do not develop GvHD. <h3>Results</h3> γδ T cells develop in BRGSF-HIS and are present in blood, spleen, lung, thymus and bone marrow. In blood, TCRγδ⁺ cells frequency in blood is variable (intra and inter-donor) and represent 3–5% of CD3⁺ cells in average. Vδ1, Vδ2 and Vδ3 are detected in blood and organs, and, as expected, Vδ1 and Vδ3 frequencies are increased in tissues compared to blood. A Vδ1-targeting agent induced ex vivo increase on activation markers CD25, 4-1BB, and CD69 expression, while decreasing CD27, a naïve gd T marker, suggesting that Vδ1 T cells developed in the model are functional. Similarly, an ‘Expander’ targeting Vγ9 significantly increased Vγ9 expressing cells frequencies. Additionally, the expression of cell activation marker CD25 increased, as well as the serum levels of perforin and INF-γ in mice treated with the expander. Interestingly, γδ T cells were recruited into the tumor microenvironment of the triple negative breast cancer line MDA-MB-231 and the colorectal adenocarcinoma HT29. The recruitment of γδ T cells into the TME suggests that therapies designed to expand and activate γδ T cells could be assessed in BRGSF-HIS mice. Investigation of efficacy of γδ T cells still remains to be investigated in the model. <h3>Conclusions</h3> The development of functional γδ T cells in BRGSF-HIS mice brings a new perspective on the assessment of therapies targeting this cell population in humanized mouse models. <h3>Reference</h3> Labarthe L, Henriquez S, Lambotte O, Di Santo JP, Le Grand R, Pflumio F, ArcangeliM-L, Legrand N, Bourgeois C. Exhaustion and senescence marker profiles on human T cells in BRGSF-A2 humanized mice resemble those in human samples. <i>J Leukoc Biol</i> 2020;<b>107</b>(1):27–42. <h3>Ethics Approval</h3> This study was conducted in compliance with CEE directive 86/609 of 24th November 1986 on the harmonization of laws, regulations or administrative provisions relating to the protection of animals used for experimental or other scientific purposes. It was also conducted in compliance with the French law, décret n° 87.848 of 19th October 1987 modified by the décret n° 2001-464 of 29th May 2001 and the décret n° 2001-486 of the 6th June 2001. From 1st February 2013, the CEE directive 2010/63/UE of 22nd September 2010 and the French décret n° 2013-118 of 1st February 2013 were applied. The study was performed in non-GLP conditions.