Ninomiya S, Narala N, Huye L, Yagyu S, Savoldo B, Dotti G et al. Tumor indoleamine 2,3-dioxygenase (IDO) inhibits CD19-CAR T cells and is downregulated by lymphodepleting drugs. Blood. 2015;125(25):3905-3916.
Prepared by: Maran Shaker & Sai Vemula, Advance Stem Cell Graduate Course, Fall 2015
LAYMAN ABSTRACT
Immunotherapy is a type of cancer treatment designed to boost the body’s natural defenses by helping the immune system work better at destroying cancer cells. Unfortunately, cancer cells develop mechanisms to fly under the radar of immune surveillance and evade detection. However, recent advancements in research have brought exciting developments in ‘targeted’ immunotherapies, that involve engineering/modifying a patient’s own immune cells to recognize and attack tumors. Engineered receptors are expressed on the surface of these T-cells which in turn provides them with the capability to identify specific proteins on cancer cells.
This technology has served as a foundation for clinical trials in treating B-cell malignancies. In particular, a T-cell was engineered to expresses a receptor called CAR (Chimeric Antigen Receptor). This receptor is able to recognize CD19, a protein that is expressed on the cell surface of these cancers. A clinical trial was performed to evaluate the effectiveness of these CD19-CAR T cells on Acute Lymphoblastic Leukemia (ALL), Chronic Lymphoblastic Leukemia (CLL) and diffuse large B-cell Lymphoma (DLBCL). Results indicated that in ALL up to 90% complete responses were observed, while in the other two cancers the results were not as promising.
The premise of this paper was to investigate what was causing the differences in cure success rates. The authors of the study hypothesized that IDO, an enzyme found in the immunosuppressive microenvironment was the culprit. It is produced by the cancer cells and could be blocking the activity of these CAR T cells.
Experiments were done in mice and results showed that IDO was overexpressed in the cancer cells. In addition, it was IDO that reacted with an amino acid (Tryptophan) to produce certain metabolites. These metabolites then acted on CAR T cells by decreasing their immune activity and caused them to die. The researchers then used chemotherapeutic drugs (FluCy) which suppressed IDO function and found that it helped improve CART activity. Therefore helping establish a possible method of pretreating patients with this chemotherapy to inhibit IDO and modify the microenvironment so that when CD19-CART T cells are injected, they can function better.
In conclusion the authors established a relationship between IDO and inhibition of CART cells which may offer solutions for future use of CART cell therapies. However, the study raises further questions: Is IDO the only target? How are the metabolites interacting with the CAR T cells? What are the exact interactions taking place at the molecular level? These questions will require further studies and hopefully enhance CART cell therapy closer to becoming the promising cancer treatment.
SCIENTIFIC ABSTRACT
Targeted Immunotherapy utilizing CD19 specific chimeric antigen receptors (CARs) offers promising opportunities for the treatment of some malignancies but has been less promising in the treatment of chronic lymphocytic leukemia (CLL) and diffuse large B-cell lymphoma (DLBCL). The authors of the study hypothesize that this is due to Indoleamine 2,3-dioxygenase (IDO). They believe that its presence in the microenvironment suppresses the activity of CAR-expressing T cells (CARTs) and hence their antitumor function.
Immunoblot analysis revealed that only Jeko-1 cell line out of the four (Jeko, Raji, Daudi, BJAB) expressed IDO. Raji, Daudi, BJAB cell lines were not stimulated by IFN-y (known to stimulate IDO). To confirm that it was IDO causing the inhibition, Raji (an IDO negative cell line) was selected as a control. After that, the effects of inhibiting IDO in tumors treated with CD19 CARTS were evaluated. A combination therapy of 1-MT+CARTs demonstrated more dramatic tumor control. In assessing the mechanism of resistance of IDO tumors to CD19-CARTs, their results showed no direct inhibition of cytotoxic function leading them to assess the effects of KHAA (metabolites further down the Kynurenine pathway). KHAA was found to significantly inhibit CART proliferation in response to CD19-positive cells. In its absence, tumor cells were almost eliminated while in its presence tumor cells increased as well as decreased CARTs.
Furthermore, the study examined if the presence of additional costimulatory domains CD28 and 4-1BB in 2nd and 3rd generation CARs respectively, could overcome the effects of KHAA. Although the later generations have improved expansion and persistence with apparently better clinical activity in comparison to 1st generation, there was no difference in the effects of KHAA observed through the experiment regardless of the construct used. Finally the authors demonstrated that Fludarabine and Cyclophosphamide (FluCy) could inhibit expression of IDO in solid tumor cell lines. Fludarabine was shown to decrease IDO expression alone but furthermore when the FluCy combination was used. Overall, FluCy significantly improved CARTs activity against IDO-positive tumors.
Overall, it appears the study demonstrated a correlation between the presence of IDO and CART cell inhibition. However, in the evaluation of IDO expression in patient cells, the variations between ‘in Vivo’ and ‘in Vitro’ differences were not taken into account. Further histological analysis could have been performed to clarify these variations. Also, in their experiments the authors utilized the ‘two flank system’ in evaluating inhibitor function. Since they were using one mouse for two different treatments, they could have a potential issue with migration of the T-cells from one flank to the other resulting in observed inaccuracies. Finally, it appears that the monitoring time for mice post treatment was shortened, possibly due to regulatory restrictions. Therefore, further evaluation of relapse and side effects were limited.
References:
Maude S, Teachey D, Porter D, Grupp S. CD19-targeted chimeric antigen receptor T-cell therapy for acute lymphoblastic leukemia. Blood. 2015;125(26):4017-4023. |
