Abstract Introduction Cardiomyocytes derived from induced pluripotent stem cells (iPSC-CMs) have been shown to remuscularize heart tissue in large animal models (1-3). However, engraftment arrhythmias also develop during the first month of transplantation (1-3). This represents a significant barrier to translation into the clinic. Additionally, it is unclear if the effect of the iPSC-CMs is due to their direct contribution to the contractile force or if it is due to changes in the adult tissue mediated through paracrine factors. Purpose In this study we developed an in vitro model to study iPSC-CM integration with adult human tissue using the living myocardial slice (LMS). Methods Our integration model is a co-culture with iPSC-CMs seeded directly onto the LMS. The LMS are taken from non-failing donor hearts provided by NHS Blood and Transplantation through the INOAR program. We use iPSC-CMS that express either a GCaMP6f calcium indicator or an optogenetic switch (inhibitory luminopsin 4, iLMO4). The GCaMP6f cells allow us to visualize the iPSC-CM synchronization with the LMS, while the iLMO4 cells allow us to measure the direct contribution of the cells by turning their contraction off with blue light (470nm). iPSC-CMs are suspended in Matrigel diluted in support media and seeded onto the slices at a density of 2x10⁶ or 3. 5x10⁶ cells per LMS. The integration model is cultured for 3 to 5 days before contraction, propensity toward arrhythmia, and synchronization are assessed. Results In the first set of cultures we seeded GCaMP6f iPSC-CMs onto the LMS and cultured them for 5 days. At the end of the culture period the iPSC-CMs were retained on the LMS surface (LMS = 5-6, hearts = 2). The iPSC-CMs beat synchronously with the LMS during field stimulation. The LMS with iPSC-CMs also showed a significant increase in spontaneous contraction after challenge with an arrhythmia inducing pacing protocol (p0. 05). There was no significant change to contraction amplitude in the treated group compared to the control. In the second set of cultures, we seeded iLMO4 iPSC-CMs onto the LMS and cultured them for 3 days. We again observed that the iPSC-CMs were retained on the surface of the LMS at the end of culture (LMS = 17-18, hearts = 5). To isolate the contribution of the iLMO4 cells the contraction of each LMS was measured before, during and after exposure to blue light. 35% of the LMS treated with iLMO4 cells showed a non-significant decrease in contraction amplitude when exposed to blue light. The force recovered when the blue light was removed. However, in LMS treated with iLMO4 cells there was no increase in spontaneous contraction in contrast to our observations in the GCaMP6f cell treated LMS. Conclusions The integration model can be used to study changes in adult tissue after their interaction with iPSC-CMs. The use of different iPSC lines allows us to investigate different aspects of integration behaviour.
Hayman et al. (Fri,) studied this question.