Background Cancer vaccines represent a promising strategy for antitumor immunotherapy. Despite considerable research efforts, effectiveness of cancer vaccines remains a challenge. This is primarily due to relatively low immune responses against tumors stemming from issues of poor immunogenicity and the immunosuppressive microenvironment commonly found in many solid tumors. Use of an optimal adjuvant can augment immune responses against tumor antigens and guide them towards a specific adaptive immune enhancement. Dendritic cells (DC) have a key role in initiating immune responses to vaccines, often through activation of toll-like receptors (TLR). Identifying novel immunomodulatory proteins that regulate DC or TLR activation can identify novel adjuvant candidates with applications for cancer immunotherapy.

Methods We constructed a Membrane Proteome Array (MPA) encompassing ~6,000 structurally intact human membrane proteins in their native conformation (94% of the entire membrane proteome) and used it to screen for cellular proteins that can modulate response to vaccination through DCs and TLRs. To identify proteins that interact with TLRs, the library was expressed in live TLR reporter cells, and these cells were tested for response to known activators using an NF-kB-activated luciferase reporter. Separately, cells expressing the MPA were presented to DCs to identify membrane proteins that modulate DC activation as measured by upregulation of cell surface markers (CD80, CD83, and MHCII).

Results Screening of TLR2, TLR3, and TLR5 reporter cell lines identified 42 potential hits, including both known and novel regulators of TLR activation. Activators common to several TLRs were identified, as well as activators unique to individual TLRs. Screening of primary human DCs likewise identified 53 modulators of DC activation including known regulators of activation (for example CD40L) and several novel targets. Putative novel regulators of DC activation are being further investigated to determine their biological significance.

Conclusions Discovering novel immunomodulatory targets and proteins that regulate DCs and TLR activation can identify novel adjuvant candidates with targeted immune outcomes, such as immune stimulating and anti-cancer responses. This study identified novel regulators of immune activation which are being further investigated as adjuvant candidates for cancer vaccines.