While the role of the immune system in cancer development is known, its role in response to chemotherapeutic agents remains elusive. Interpatient variability in immune and chemotherapeutic cytotoxic responses is likely due to complex genetic differences. Through the use of a panel of genetically diverse mouse inbred strains, we developed a drug screening platform aimed at examining novel mechanisms underlying these chemotherapeutic cytotoxic responses on immune cells. Drug effects were investigated by comparing more selective chemotherapeutic agents such as BEZ235 and selumetinib against conventional cytotoxic agents, including doxorubicin and idarubicin. Phenotypes were quantified using flow cytometry, yielding interstrain variation for measured endpoints in different immune cells. Our flow cytometry assay produced nearly 16,000 data points that were used to generate dose response curves. The more targeted agents, BEZ-235 and selumetinib, were less toxic to immune cells than the anthracycline agents. Also, heritability for the viability of immune cells was higher for anthracyclines than the novel agents, making them ideal for genetic analysis. Using genome-wide association studies, we identified loci that contributed to the sensitivity of doxorubicin and idarubicin in immune cells. We identified 8 QTL containing 25 potential candidate genes. Of particular interest, App, encoding for amyloid beta precursor protein, was identified under a peak on chromosome 16 (p = 5.01x10-8) in T-cells exposed to idarubicin. Dose response curves verified that T-cells in App knockout mice were more sensitive to idarubicin than those of C57BL/6J control mice (p = 0.01). Using a cellular screening approach, we identified and subsequently validated a gene candidate encoding for amyloid beta precursor protein in T-cells exposed to idarubicin. The literature has suggested a role for App in in vitro and in vivo cytotoxicity to anticancer agents; the overexpression of App enhances resistance, while the knockdown of this gene is deleterious to cell viability. In the future, we aim to perform mechanistic studies in primary and immortalized immune cells, validate additional candidate genes, and, ultimately, to translate our findings to in vivo and human studies.