Currently, HIV infection is studied in mouse models where human stem cells are transplanted into mice, serving as targets for HIV-1 infection. These models are used extensively for investigation of the impact of gene modification of stem cells with anti-HIV gene therapeutics. One limitation of these models is that the transplant with anti-HIV gene-modified human stem cells is established first then followed by HIV-1 infection. This model is the reverse order of a therapeutic transplant in humans where individuals are transplanted with anti-HIV gene-modified stem cells after HIV-1 infection. We propose to develop a more representative model where we first transplant stem cells to establish a human immune system in mice, then infect with HIV-1, and then conduct a second transplant with gene-modified human stem cells. This model would more closely mimic the human clinical situation. We have successfully identified conditions for two transplants in mice and are now evaluating whether this new humanized mouse model can be used to study protection from HIV-1 by anti-HIV gene modification of stem cells.
The most common current models for anti-HIV-1 gene therapy is through the use of humanized mice, immunodeficient animals into which human cells are engrafted. Evaluation of anti-HIV-1 gene therapy in animal models has been performed by HIV-1 challenge AFTER transplant with gene modified HSPC. This experimental design allows us to gain important data in a relatively simple setting. However, the clinical application of gene therapy will be in patients already infected with HIV-1. Thus, it is important to test the impact of HIV-1 infection on the success of gene modified HSPC engraftment and differentiation and through control of HIV-1 in previously infected humanized mice. We tested a new mouse model whereby the first transplant of CD34+ cells allows human hematopoietic cell reconstitution and provides human cells for HIV-1. After HIV-1 is established, a second transplant is conducted using anti-HIV-1 gene modified CD34+ cells and thymus tissue. We find that the timing of the second transplant is important in order to maintain the integrity of the thymic organoid. In this system, repopulation of human CD45+ cells, CD3+, CD4+, CD8+ cells occurs efficiently. In HIV-1 infected animals, CD4+ cells are decreased relative to uninfected control animals. Under these conditions, we observe protection from HIV-1 by the transplant of genetically modified CD34+ cells. These studies provide the basis for a new model which should be useful for understanding and evaluating the efficacy of anti-HIV-1 gene modification of hematopoietic stem cells.