Tumor infiltrating Foxp3+ Tregs recognize synthesized but not naturally available cancer neoantigens

In new paper in @SciImmunology, Steven Rosenberg's group from @NIH asks why are #Tregs accumulate in tumor tissues and if it has something to do with #cancer #antigen recognition. But how to study #Foxp3+ Tregs in humans? No reliable surface marker exist yet.

— David Usharauli (@3DiMMUNE) January 14, 2019

1. First, they sorted fix/perm T cells from #tumor samples based on Foxp3+ expression to separate #Tregs from non-Tregs and sent the sorted samples to @AdaptiveBiotech (this is what all do now days looks like) for deep #TCR #sequencing and alpha/beta TCR #pairing.

— David Usharauli (@3DiMMUNE) January 14, 2019

2. They found differences between Treg-TCRs usage and non-Treg TCR usage. OK. Then what? #Sequencing or even TCR pairing by itself have no value unless one knows what these #TCR recognize. Many labs don't even bother to do anything about it, but #Rosenberg's people did.

— David Usharauli (@3DiMMUNE) January 14, 2019

3. To do it, they took top #Foxp3+ #Treg TCRs pairs and #transfected them individually into #autologous T cells and tested their #reactivity to autologous tumor samples. Some #TCR specifically recognized something in autologous tumor samples. They thought it must #antigen. pic.twitter.com/fbj8esBJSq

— David Usharauli (@3DiMMUNE) January 14, 2019

4. To identify antigen recognized by Treg TCRs, they used whole-#exome and RNA sequencing (RNA-seq) to detect somatic mutations and make mutant peptide pool. Indeed one Treg TCR from one patient and another Treg TCR from another patient recognized mutant #annexin A1 and #CCL5. pic.twitter.com/FRiibvwYTX

— David Usharauli (@3DiMMUNE) January 14, 2019

5. But here is the twist. None of these #Treg #TCRs recognized autologous tumor samples. Interestingly, for #annexin A1 the authors suggested its expression was too low in tumor samples and for #CCL5 they found that tumor cells actually do not express CCL5 at #RNA level.

— David Usharauli (@3DiMMUNE) January 14, 2019

Basically, Treg TCR could recognize lab #synthesized #mutant peptides from patient samples but not natural #tumor cells. So, the authors ended up back in square one. #Tregs go to tumor tissues but the methods we have right now does not allow us to know what Ag they see it there.

— David Usharauli (@3DiMMUNE) January 14, 2019

Selective Tregs elimination within tumor using CD25 antibody coupled to near-infrared photoimmunotherapy

Regulatory T cells (Tregs) inhibit immune responses. When considering autoimmune diseases or allergies, this function of Tregs has beneficial effect on host. The same function, however, could be "hijacked" by tumors to evade immune destruction. So far, selective depletion of tumor-associated Tregs has not been achieved in clinical settings.

New paper in Science Translational Medicine suggested novel approach to eliminate tumor-associated Tregs: application of anti-CD25 F(ab)2 fragments coupled to photo-active silica-phthalocyanine dye (IR700)  and exposed to near-infrared photo-immunotherapy (NIR-PIT). 

First, in vitro experiments showed that when CD25+ cells are exposed to anti-CD25 F(ab)2-IR700 and subjected to NIR-PIT, they undergo cell death.

Since tumors accumulate high frequency of Tregs, the authors conducted NIR-PIT experiments in vivo. When tumor-challenged mice were exposed to anti-CD25 F(ab)2-IR700 and subjected to NIR-PIT, the authors observed temporal delay in tumor growth and improved survival. 

Of note, tumors located at the distant sites away from direct exposure of NIR-PIT also display growth delay after anti-CD25 F(ab)2-IR700/NIR-PIT application, indicating system-wide after-effect of local elimination of Tregs by NIR-PIT.

Finally, the authors found that anti-tumor effect of anti-CD25 F(ab)2-IR700/NIR-PIT application was mediated by IFN-gamma derived from CD8 T and NK cells.

In summary, the authors claim that this less invasive procedure could selectively eliminate CD25+ Tregs (but not effector T cells) in tumors  and improve survival of tumor-challenged host.

David Usharauli

T cell compatible cancer chemotherapy synergizes with cancer adjuvant vaccine

Nowadays it is well acknowledged that optimal cancer treatment would require multi-pronged approach, for example, combining cancer chemotherapy with cancer antigen-specific vaccine to boost tumor-specific T cell response. However, such combination is not always feasible since (a) both tumor and activated T cells are highly proliferative cell types and (b) vast majority of chemotherapy drugs target cellular replication machinery. Basically, it is matter of trial and error to find T cell compatible chemotherapy drugs.

Such combination was recently described in new paper published in Science Translational Medicine. Here, the authors showed that cervical cancer treatment with CarboTaxol (carboplatin + paclitaxel) synergizes with therapeutic T cell vaccine that consisted of HPV16 overlapping synthetic long peptides (HPV16-SLPs) admixed with adjuvant Montanide ISA-51.

Most cervical cancers in humans are induced by human papillomavirus type 16 (HPV16). Initially, the authors showed that CarboTaxol synergized with HPV16-SLP vaccination in HPV16-positive TC-1 tumor-bearing mouse model.

Next, the authors noticed that CarboTaxol [and vaccine too] reduced level of CD11b^highGr1^high myeloid [suppressor] population within tumor tissue.

Similar depletion of myeloid population was observed in blood samples of cervical cancer patients undergoing CarboTaxol therapy.

In fact, CarboTaxol treatment cycles significantly improved T cells proliferation in response to minor [bacterial recall antigen mixture, MRM)] and major HLA antigens [MLR].

Finally, combining CarboTaxol treatment with HPV16-SLP vaccination improved T cell stimulation in response to HPV16 antigens E6/E7.

In summary, this study indicates that CarboTaxol chemotherapy augments, rather than inhibits, tumor-specific T cell priming in response to HPV16-SLP vaccination.

David Usharauli