Long-term in-vivo tumorigenic assessment of human culture-expanded adipose stromal/stem cells

Abstract

After more than a decade of extensive experimentation, the promise of stem cells to revolutionize the field of medicine has negotiated their entry into clinical trial. Adipose tissue specifically holds potential as an attainable and abundant source of stem cells. Currently undergoing investigation are adipose stem cell (ASC) therapies for diabetes and critical limb ischemia, among others. In the enthusiastic pursuit of regenerative therapies, however, questions remain regarding ASC persistence and migration, and, importantly, their safety and potential for neoplasia. To date, assays of in vivo ASC activity have been limited by early end points. We hypothesized that with time, ASCs injected subcutaneously undergo removal by normal tissue turnover and homeostasis, and by the host's immune system. In this study, a high dose of culture expanded ASCs was formulated and implanted as multicellular aggregates into immunocompromised mice, which were maintained for over one year. Animals were monitored for toxicity, and surviving cells quantified at study endpoint. No difference in growth/weight or lifespan was found between cell-treated and vehicle treated animals, and no malignancies were detected in treated animals. Moreover, real-time PCR for a human specific sequence, ERV-3, detected no persistent ASCs. With the advent of clinical application, clarification of currently enigmatic stem cell properties has become imperative. Our study represents the longest duration determination of stem cell activity in vivo, and contributes strong evidence in support of the safety of adipose derived stem cell applications.

Conflict of interest statement

Disclosure of potential conflicts of interest: Dr. Adam Katz receives royalties from patents related to adipose stem cells.

Copyright © 2011 Elsevier Inc. All rights reserved.

Figures

Figure 1. Treated and control weight over time, with standard error

Control and treated animal weights followed a similar trend over time in both in both (a) non-cryopreserved and (b) cryopreserved groups. There was no significant difference between treated and control group weights by student’s T-test.

Figure 1. Treated and control weight over time, with standard error

Control and treated animal weights followed a similar trend over time in both in both (a) non-cryopreserved and (b) cryopreserved groups. There was no significant difference between treated and control group weights by student’s T-test.

Figure 2. Gross organ abnormalities

(a) Treated Ms39 with nodular spleen, (b) control Ms435 with enlarged, nodular spleen.

Figure 2. Gross organ abnormalities

(a) Treated Ms39 with nodular spleen, (b) control Ms435 with enlarged, nodular spleen.

Figure 3. Liver histology, hematoxylin and eosin

(a) Control Ms435 (shown with 1 mm reference) with lymphoma (arrow), (b) Treated Ms42 (shown with 200 um reference) with evidence of peliosis (arrow), a vascular condition of unknown etiology characterized by randomly distributed blood filled sinuses throughout the liver, and necrosis.

Figure 3. Liver histology, hematoxylin and eosin

(a) Control Ms435 (shown with 1 mm reference) with lymphoma (arrow), (b) Treated Ms42 (shown with 200 um reference) with evidence of peliosis (arrow), a vascular condition of unknown etiology characterized by randomly distributed blood filled sinuses throughout the liver, and necrosis.

Figure 4. RT-PCR for ERV-3

Two standard curves were used, (a) one consisting of varied concentrations of human cells only, and the other (b) consisting of varied concentrations of human cells mixed with mouse tissue, either lung, spleen or skin and subcutaneous tissue. Both the human cell only standards and the relevant tissue standard curve were included in each PCR run.

Figure 4. RT-PCR for ERV-3

Two standard curves were used, (a) one consisting of varied concentrations of human cells only, and the other (b) consisting of varied concentrations of human cells mixed with mouse tissue, either lung, spleen or skin and subcutaneous tissue. Both the human cell only standards and the relevant tissue standard curve were included in each PCR run.