From killers to thieves
NK cells steal PD-1 from cancer cells and are inactivated
Peter Kazimirov, PCR.news
It was previously shown that the PD-1 receptor suppresses the activity of natural killer cells (NK), so that these cells contribute to the effectiveness of therapy with immune checkpoint inhibitors in a mouse model. However, the authors were confused by the fact that normally NK does not express PD-1. In a new paper, the same group of scientists showed that NK receive the PD-1 receptor due to trogocytosis, "stealing" it from cancer cells.
Article by Hasim et al. When killers become thieves: Trogocytosed PD-1 inhibits NK cells in cancer is published in the journal Science Advances.
Trogocytosis is a process in which a cell captures a fragment of the cell membrane of another cell and includes it in its own. So the membrane proteins carried by the victim cell end up on the membrane of the hunter cell.
Cancer cells are indicated in green, the arrow points to the NK cell.
First of all, the authors confirmed that NK receives PD-1 from cancer cells. To do this, the scientists used a line of mouse lymphoma cells RMA. They obtained a recombinant RMA cell line expressing PD-1 and the Thy-1.1 marker protein, as well as a PD-1 knockout line (Pdcd-/-). When stained, cells carrying both proteins turned blue, and cells carrying only Thy-1.1 turned purple. Next, the scientists cultured RMA cells together with NK. NK itself was not stained by any of the proteins. But NK cultured with Pdcd+/+ RMA cells were stained by both PD-1 and Thy-1.1, and cultured with Pdcd-/- — only by Thy-1.1.
Scientists have also confirmed the need for intercellular contact for protein transfer. Those NK that were separated from RMA cells by a barrier during cultivation, as well as those that were cultured in a supernatant in which RMA cells were previously located, were not stained by any of the proteins.
Since there is no specific way to inhibit the process of trogocytosis, scientists disrupted the synthesis of ATP and polymerization of actin. In both cases, NK was not stained by any of the proteins, even when co-cultured with RMA cells. Scientists have also confirmed the fact of trogocytosis with several additional experiments with staining of membrane lipids and proteins.
Next, the authors determined which receptors regulate the process of trogocytosis. The first assumption of scientists was the interaction of PD-1 on cancer cells and PD-L1 on NK. However, saturation of the culture with antibodies blocking PD-L1 did not lead to a stop of trogocytosis, just like the PD-L1 knockout. Then scientists turned their attention to SLAM receptors, a group of proteins expressed by immune cells and involved in intercellular interactions, such as the presentation of antigens. SLAM receptors are normally expressed by both NK and T- and B-lymphocytes. To test the role of SLAM receptors in trogocytosis, scientists performed a knockout of the SLAM locus in immune cells, which were then cultured with RMA cells. In this experiment, scientists observed a violation of trogocytosis in both NK and T- and B-lymphocytes.
The scientists also decided to check whether trogocytosis takes place in vivo. To do this, Pdcd+/+ and Pdcd-/- mice were injected with RMA or RMA-Pdcd-/- cells. When the tumor size reached 300 mm3, scientists selected NK from cancer tissues and stained them. In all cases, NK from cancerous tissues were stained by Thy-1.1. Only NK obtained from animals injected with Pdcd+/+ RMA cells were stained by PD-1, regardless of whether the animal itself expresses PD-1.
The authors demonstrated that PD-1 capture inhibits NK activity in vivo — administration of Pdcd-/-RMA-S-Pdl cells from previous work to Pdcd-/-mice significantly slowed tumor growth. At the same time, in vitro growth of Pdcd-/- RMA-S-Pdl cells was not slowed down.
Finally, scientists confirmed the fact of human trogocytosis in a number of clinical cases, using CD138 protein expressed by cancer cells as a marker, but not NK.
Portal "Eternal youth" http://vechnayamolodost.ru