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High resolution, non-invasive longitudinal live imaging of immune responses

Midhat H. Abdulreda¹, Gaetano Faleo¹, R. Damaris Molano¹, Maite Lopez-Cabezas¹, Judith Molina¹, Yaohong Tan³, Oscar Ron Echeverria¹, Elsie Zahr-Akrawi¹, Rayner Rodriguez-Diaz¹, Patrick Edlund², Ingo Leibiger², Allison Bayer¹, Victor Perez³, Camillo Ricordi^1,2, Alejandro Caicedo¹, Antonello Pileggi¹, Per-Olof Berggren^1,2

¹Diabetes Research Institute, University of Miami, Miami, FL, United States; ²Rolf Luft Center for Diabetes Research and Endocrinology, Karolinska Institutet, Stockholm, Sweden; ³Bascom Palmer Eye Institute, University of Miami, Miami, FL, United States

In vivo imaging has emerged as an indispensible tool in biological research. Intravital studies have revealed the significance of immune cell dynamics in the lymph nodes during immune responses. However, little is currently known about the in vivo behavior of T-lymphocytes in peripheral organs, including grafted tissues such as pancreatic islets. This has been primarily due to the combination of the limited noninvasive access to the same tissue in the living animal longitudinally and the relatively low spatial resolution of existing intravital imaging modalities. Here, we noninvasively studied the in vivo movement dynamics of T-lymphocytes that infiltrate pancreatic islets after transplantation. MHC-mismatched DBA/2 mouse islets were transplanted without immunosuppression into the anterior chamber of the eye (ACE) of C57BL/6(B6.129P2-Cxcr6tm1Litt/J) recipients expressing GFP in effector and memory T-lymphocytes. Rejection was characterized by progressive accumulation of GFP-positive lymphocytes paralleled by loss of volume and function of allogeneic islets in the ACE. In vivo analysis of morphology and dynamic behavior of islet-infiltrating effector T-lymphocytes revealed a “ruffled” phenotype of cytotoxic T-lymphocytes that predominated during the effector phase of rejection. Ruffled cells engaged in contacts with other surrounding T-lymphocytes and target islet cells simultaneously. The ruffled phenotype was characterized by a significantly increased but constrained dynamic behavior within the islet allografts. In summary, our results demonstrate that intraocular transplantation enables: (1) longitudinal, non-invasive monitoring of transplanted tissuesin vivo; (2)in vivo cytolabeling to assess cellular phenotype and viabilityin situ; (3) local intervention by topical application or intraocular injection; and (4) real-time tracking of infiltrating immune cells in the target tissue.