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Contact-dependent modulation of the human immune response to pig cells by adipose-derived mesenchymal stem cells (AdMSC) from GTKO/CD46 pigs

Goutham Kumar¹, Hidetaka Hara¹, Cassandra Long¹, David Ayares², David K.C. Cooper¹, Mohamed Ezzelarab¹

¹Thomas E. Starzl Transplantation Institute, Pittsburgh, PA; ²Revivicor Inc., Blacksburg, VA, United States

Introduction: The immunomodulatory and anti-inflammatory effects of MSC could prove to be a potential therapeutic approach for prolongation of survival of cell xenotransplantation. Genetically-modified pigs could be an abundant source of organs and cells, but also of donor-specific MSC.

Methods: pMSC were isolated from adipose tissue of α1, 3-galactosyltransferase gene knock-out pigs transgenic for human (h) CD46 [GTKO/hCD46]). pMSC were identified by differentiation and by surface phenotype by flowcytometry (FCM). Naïve human and sensitized baboon IgM/IgG binding to GTKO/hCD46 pAdMSC and GTKO pig aortic endothelial cells (pAEC) was measured by FCM. The immunomodulation of human peripheral blood mononuclear cell (PBMC) responses to GTKO pAEC by GTKO/hCD46 pAdMSC was compared with commercially-available hAdMSC by measuring 3H-thymidine uptake. The supernatants from the MSC cultures were used to determine the role of soluble factors.

Results: GTKO/hCD46 pAdMSC (i) did not express Galα1, 3Gal (Gal), but expressed hCD46, (ii) differentiated into chondroblasts, osteoblasts and adipocytes, (iii) expressed CD29, CD44, CD90, and CD105, but did not express CD45 or CD31, (iv) expressed lower levels of SLA I and II than pAEC before and after pIFN-γ stimulation (p<0.001), and (v) expressed costimulatory molecules (CD80, CD86) constitutively. Naïve human and sensitized baboon antibody binding to GTKO pAEC was greater than to GTKO/hCD46 pAdMSC. The proliferation of human PBMC to GTKO/hCD46 pAdMSC and hAdMSC stimulators was similar, and both were significantly lower than to GTKO pAEC (p<0.05). Human PBMC proliferation to GTKO pAEC was equally suppressed by GTKO/hCD46 pAdMSC and hAdMSC (p<0.01). The supernatant from GTKO/hCD46 pAdMSC did not suppress the human xenoresponse to GTKO pAEC.

Conclusions: (1) Genetically-modified pAdMSC are less immunogenic than GTKO pAEC, and no more immunogenic than hAdMSC. (2) The immunomodulatory function of pAdMSC is comparable to that of hAdMSC and is contact-dependent. (3) Genetically-modified pMSC may provide a potential therapy in cell xenotransplantation.