Delivery of natural killer (NK) cells using heparin-hyaluronic acid hydrogel

Abstract

As cell-based immunotherapy becomes more popular nowadays, both T cells and natural killer (NK) cells are used to recognize and destroy the “stressed” or virus-infected cells. Delivering immune cells intratumorally, especially to treat solid tumors is still challenging because of the poor ability of NK cells to reach tissues, injected cells may spread to other areas or even they could not be able to migrate to the site of infection. Moreover, the low cell viability after injection also becomes part of the problem. Hyaluronic acid as a major component of the extracellular matrix has also shown a positive result as it could provide the multi-aggregation of NK cells. In our previous study, heparin, which has great binding sites with various types of growth factors and cytokines has successfully promoted the attachment and proliferation of stem cells. Taking advantage of both natural polymers, a photocrosslinked hydrogel between thiolated heparin and methacrylated heparin was utilized to deliver NK cells. After crosslinking, the bulk gel was crushed using a tissue homogenizer to produce an injectable size hydrogel and as a result, the shape of both 2% and 5% of Hep-HA crushed gel could be maintained after injection through 21G and 23G needles. The viability of NK cell-loaded Hep-HA gel also did not show a significant difference before and after injection through a 23G needle. When seeded with NK92MI cells, Hep-HA hydrogel could provide a non-toxic environment for the cultivation of NK cells. In addition, Hep-HA crushed gel could mediate a sustained and controlled release of NK cells as 84.8% and 50.7% of NK cells could cumulatively release from 2% and 5% Hep-HA crushed gel. Our Hep-HA crushed gel could also maintain the cytotoxicity of NK cells even after 1 day and 3 days of cultivation. Furthermore, IL-15 was incorporated to enhance the immunotherapeutic effect of NK cells. As the results, priming NK cells inside Hep-HA gel could increase the cytotoxicity of NK cells compared to NK cells primed in the culture media.