Understanding the Synergy of NKp46 and Co-Activating Signals in Various NK Cell Subpopulations: Paving the Way for More Successful NK-Cell-Based Immunotherapy

Abstract

The NK cell population is characterized by distinct NK cell subsets that respond differently to the various activating stimuli. For this reason, the determination of the optimal cytotoxic activation of the different NK cell subsets can be a crucial aspect to be exploited to counter cancer cells in oncologic patients. To evaluate how the triggering of different combination of activating receptors can affect the cytotoxic responses of different NK cell subsets, we developed a microbead-based degranulation assay. By using this new assay, we were able to detect CD107a+ degranulating NK cells even within the less cytotoxic subsets (i.e., resting CD56bright and unlicensed CD56dim NK cells), thus demonstrating its high sensitivity. Interestingly, signals delivered by the co-engagement of NKp46 with 2B4, but not with CD2 or DNAM-1, strongly cooperate to enhance degranulation on both licensed and unlicensed CD56dim NK cells. Of note, 2B4 is known to bind CD48 hematopoietic antigen, therefore this observation may provide the rationale why CD56dim subset expansion correlates with successful hematopoietic stem cell transplantation mediated by alloreactive NK cells against host T, DC and leukemic cells, while sparing host non-hematopoietic tissues and graft versus host disease. The assay further confirms that activation of LFA-1 on NK cells leads to their granule polarization, even if, in some cases, this also takes to an inhibition of NK cell degranulation, suggesting that LFA-1 engagement by ICAMs on target cells may differently affect NK cell response. Finally, we observed that NK cells undergo a time-dependent spontaneous (cytokine-independent) activation after blood withdrawal, an aspect that may strongly bias the evaluation of the resting NK cell response. Altogether our data may pave the way to develop new NK cell activation and expansion strategies that target the highly cytotoxic CD56dim NK cells and can be feasible and useful for cancer and viral infection treatment.

The Role of Natural Killer Cells in Autoimmune Diseases

“…The majority of human NK cells in the peripheral blood is the subset which is best characterized by diminished expression of CD56 and express high levels of CD16 ( Figure 1 ) ( 44 , 45 ). Several recent studies have suggested that unlike this traditional model, CD16 + CD56 dim and CD16 - CD56 bright NK cells may also originate from separate lineages ( 36 – 38 , 45 , 46 ).…”

“…Meanwhile, mature NK cells gain self-tolerance and effector-functions by loss of CD34 and ckit accompanied by sequential expression of CD56, CD94, and the killer C-type lectin receptor (CD161) (24,32,33). Mature NK cells can progress into 2 final developmental stages, with respect to the expression of CD56 and CD16 (34)(35)(36)(37)(38).…”

Engineering CAR-NK cells: how to tune innate killer cells for cancer immunotherapy

“…An alternative method to promote NK-cell expansion without feeder cells is monoclonal antibodies (mAb), such as the combination of anti-CD52 and anti-CD3, which demonstrated a favorable growth of NK-cells while suppressing CD4 + T-cells from peripheral blood mononuclear cell (PBMC) [ 57 ]. Moreover, activation using microbeads covered with antibodies against various NK receptors, such as NKp46, 2B4, DNAM-1, CD2, and CD18, is another strategy that can improve NK-cell expansion and activation [ 58 ].…”

Research Progress on NK Cell Receptors and Their Signaling Pathways

“…NKp46 acts as a coactivation receptor which triggers NK cell cytotoxicity by synergistic effects with other activating receptors. Researches confirmed that NKp46 could coengage with 2B4, CD2, NKG2D, and DNAM-1, transmitting activation signals to enhance the Ca 2+ flux of NK cells further [ 52 , 53 ]. However, we still do not know if synergistic signals of NKp46 and other coactivation receptors are the same as the synergistic signals of NKG2D and 2B4.…”