In vitro T lymphopoiesis: a model system for stem cell gene therapy for AIDS

Stable introduction of therapeutic genes into hematopoietic stem cells has the potential to reconstitute immunity in individuals with HIV infection. However, many important questions regarding the safety and efficacy of this approach remain unanswered and may be addressed in a non-human primate model. To facilitate evaluation of expression of foreign genes in T cells derived from transduced hematopoietic progenitor cells, we have established a culture system that supports the differentiation of rhesus macaque and human CD34+ bone marrow derived cells into mature T cells. Thymic stromal monolayers were prepared from the adherent cell fraction of collagenase digested fetal or neonatal thymus. After 10-14 days, purified rhesus CD34+ bone marrow-derived cells cultured on thymic stromal monolayers yielded CD3+CD4+CD8+, CD3+CD4+CD8-, and CD3+CD4-CD8+ cells. Following stimulation with mitogens, these T cells derived from CD34+ cells could be expanded over 1,000-fold and maintained in culture for up to 20 weeks. We next evaluated the ability of rhesus CD34+ cells transduced with a retroviral vector containing the marker gene neo to undergo in vitro T cell differentiation. CD34+ cells transduced in the presence of bone marrow stroma and then cultured on rhesus thymic stroma resulted in T cells containing the retroviral marker gene. These studies should facilitate both in vitro and in vivo studies of hematopoietic stem cell therapeutic strategies for AIDS.