Lipid Nanoparticle-Mediated Combinational mRNA Vaccine for Multiple Myeloma: The Next Stage of Cancer Immunotherapy

Cancer vaccines are emerging as promising therapies to not only prevent cancer but to treat cancer. Vaccines train cytotoxic T cells (CTLs) to target tumor associated antigens to kill cancer cells. Cancer vaccines, especially mRNA vaccines, can be rapidly produced and express the full protein, enabling a diverse immune response against multiple epitopes of that protein. Here, we developed a therapeutic cancer vaccine for multiple myeloma (MM), an incurable cancer of the plasma cells. We targeted B cell maturation antigen (BCMA) protein, as it’s considered a therapeutic target for MM because of its high and selective expression on the MM cell surface.

We first packaged the BCMA mRNA into lipid nanoparticles (LNPs), which is an FDA-approved delivery mechanism that can efficiently deliver the mRNA to antigen-presenting cells, such as dendritic cells (DCs). We also encapsulated a potential Toll-like receptor (TLR) agonist, polyinosinic:polycytidylic acid (Poly I:C) in LNPs to further elicit the immune response. We found that the resulting particles were in the range of ~100 nm in size and had >96% loading for both BCMA and Poly: IC LNPs. The switch in surface charge from negative at physiological pH (7.4) to positive in the acidic endosomal environment confirmed the efficient endosomal escape of the mRNA into the cytosol. In addition, LNPs were stable during incubation in human serum for 2h at 37°C, unlike free mRNA. Finally, we confirmed that LNPs loaded with mRNA encoding GFP succeeded in expressing GFP within the cytosol of DCs, as compared to free mRNA.

To assess our vaccine in vitro, we isolated monocyte-derived dendritic cells and naive T cells from the same healthy human donor, and after treatment, the DCs were co-cultured with T cells for 5 days. We measured carboxyfluorescein succinimidyl ester (CFSE) dilution percentage to evaluate T cell proliferation and found 71.9±4.0% and 51.7±4.3% of CFSE dilution for BCMA+ Poly: IC LNPs and BCMA LNPs, respectively, as compared to free mRNA (9.7±4.0%, p<0.05). We found that the CTLs from this co-culture effectively lysed U266 cells but not BCMA-KO cells (p<0.05). An ELISpot assay found an enhanced (p<0.05) spot count (SFC per million cells) for IFNɣ and TNFα for packaged BCMA mRNA and for the combination treatment with poly: IC in comparison to free BCMA mRNA.

To assess the biodistribution, we loaded the LNPs with DiR dye and further to evaluate in vivo translational potential, mRNA encoding firefly luciferase (fLuc) was packaged and treated C57BL/6 mice. Hematoxylin and eosin (H&E) staining of major organs showed a good safety profile. The higher percentages of DiR loaded LNPs accumulation was observed in liver and spleen for both intravenous and intramuscular injection as determined by % DiR dye uptake using FACs. The splenic accumulation of BCMA LNPs resulted in the activation of the DCs (p<0.05) with and without adjuvant Poly: IC, as evaluated by DC activation markers CD40 and CD80 using FACs and immunofluorescence (IF) staining of the spleen. When BCMA LNPs were treated alone or in combination with adjuvant, there was a significant increase in BCMA-specific splenic CD8-T cells, as determined by tetramer staining using flow cytometry. A similar result was noticed for the infiltration of CD3 and CD8 T cells, while splenic tissue was analysed by IF multiplexing. Splenic T cells isolated from treated C57BL/6 mice efficiently killed murine 5TGM1 cells. In all instances, the adjuvant further elicited the immune response induced by BCMA LNPs.

In conclusion, our findings lay the framework for the development of therapeutic cancer vaccines and aim to establish MM therapeutic cancer vaccination as a potential immunotherapeutic tool in the clinic, ultimately saving patient lives.