Toward Humanization of the Pig; Boldly Going where Only Mice have Gone Before

We are expanding the biomedical utility of the naturally occurring severe combined immune deficient (SCID) Yorkshire pigs at Iowa State University. Specifically, a major biomedical application of SCID mammals is creating “humanized” animals that harbor a human immune system and that can be used for testing vaccine efficacy and studying host interactions with primate-specific pathogens. Two litters of piglets were created by mating SCID carrier females to an allogenic bone marrow transplant-rescued SCID boar. Of 20 live births, 13 piglets had the SCID genotype. At seven days of age, seven piglets were injected with human cord blood affinity-purified CD34+ cells (approximately 5 x 10⁵cells per kg) of varying purity (60-98% CD34+). Twenty-four hours prior to cell transfer, three recipients received mild myelosuppressive conditioning with busulfan. Evidence of human hematopoietic engraftment was tested every two weeks via fluorescence-activated cell sorting analysis of whole blood using Biotin-labeled human anti- CD45. A majority of transplanted pigs exhibited a diffuse erythematous rash similar to human grade 1 acute graft versus host disease. Several pigs were diarrhetic and skin biopsies confirmed CD3+ lymphocyte infiltration in both pigs tested. Of note, skin lesions were more pronounced in animals transplanted with grafts containing a lower percentage of human CD34+ cells.  At necropsy, flow cytometry on isolated cells from bone marrow of transplanted pigs will be conducted, as well as Q-PCR for human mitochondrial DNA, to quantify engraftment of human hematopoietic lineages.