The goal of this protocol is to show the protocol for reprogramming melanoma tumor-infiltrating lymphocytes into induced pluripotent stem cells.
Adoptive transfer of ex vivo expanded autologous tumor-infiltrating lymphocytes (TILs) can mediate durable and complete responses in significant subsets of patients with metastatic melanoma. Major obstacles of this approach are the reduced viability of transferred T cells, caused by telomere shortening, and the limited number of TILs obtained from patients. Less-differentiated T cells with long telomeres would be an ideal T cell subset for adoptive T cell therapy;however, generating large numbers of these less-differentiated T cells is problematic. This limitation of adoptive T cell therapy can be theoretically overcome by using induced pluripotent stem cells (iPSCs) that self-renew, maintain pluripotency, have elongated telomeres, and provide an unlimited source of autologous T cells for immunotherapy. Here, we present a protocol to generate iPSCs using Sendai virus vectors for the transduction of reprogramming factors into TILs. This protocol generates fully reprogrammed, vector-free clones. These TIL-derived iPSCs might be able to generate less-differentiated patient- and tumor-specific T cells for adoptive T cell therapy.
Cellular reprogramming technology that allows generation of induced pluripotent stem cells (iPSCs) via overexpression of a defined set of transcription factors holds great promise in the field of cell-based therapies1,2. These iPSCs exhibit transcriptional and epigenetic features and have the capacity for self-renewal and pluripotency, similarly to embryonic stem cells (ESCs)3-5. Remarkable progress made in reprogramming technology over the past decade has allowed us to generate human iPSCs even from terminally differentiated cells, such as T cells6-8. T cell-derived iPSCs (TiPSCs) retain the same rearranged configuration of T cell receptor (TCR) chain genes as the original T cells, which allows regeneration of antigen-specific T cells from TiPSCs9-11.
Nearly 80% of melanoma-infiltrating lymphocytes (TILs) obtained from a patient's tumor specifically recognize tumor-associated antigens and maintain cytotoxicity against the original cancer cells12. Notably, the expression of programmed cell death protein-1 (PD-1) on TILs was found to identify the autologous tumor-reactive repertoire, including mutated neoantigen-specific CD8+ lymphocytes13. Adoptive transfer of ex-vivo expanded autologous TILs in combination with preparative lymphodepleting regimens and systemic administration of Interleukin-2 (IL-2) can cause substantial regression of metastatic melanoma in subsets of patients14. Despite encouraging results in preclinical models and in patients, poor survival of infused T cells and the existence of immune suppressive pathways appear to compromise the full potential of adoptive T cell therapy. Current clinical protocols require extensive ex vivo manipulation of autologous T cells in order to obtain large numbers. This results in the generation of terminally differentiated T cells that have poor survival, reduced proliferative capacity, and high levels of PD-115.
This limitation of adoptive T cell therapy can be theoretically overcome by using iPSCs that can provide an unlimited source of autologous T cells for immunotherapy. We have recently reported the reprogramming of melanoma TILs expressing high levels of PD-1 by Sendai virus (SeV)-mediated transduction of the four transcription factors, OCT3/4, SOX2, KLF4, and c-MYC16. While retrovirus vectors require integration into host chromosomes to express reprogramming genes, SeV vectors are non-integrating and are eventually eliminated from the cytoplasm. Reprogramming efficiency is much higher with a SeV system compared with lentivirus or retrovirus vectors6-8. Furthermore, SeV can specifically reprogram T cells in peripheral blood mononuclear cells (PBMCs), while some iPSC clones generated by lentivirus or retrovirus vectors can be from nonlymphoid lineages6-8. Here, we detail the procedures implemented for the isolation and activation of human melanoma TILs and for the generation of TIL-derived iPSCs using a SeV reprogramming system.
NOTE: Patients should give informed consent to participate in the Institutional Review Board and Human Pluripotent Stem Cell Committee approved study.
1. Isolation and Culture of TILs
2. Preparation of Mitomycin-C-treated SNL Feeder Cell Plate
3. Generation of iPSCs Using the Sendai Virus (SeV) Vector
4. Immunofluorescence Staining of iPSCs for SSEA3, SSEA4, TRA1-60 and TRA1-81
5. Immunofluorescence Staining of iPSCs for Oct3/4
Figure 1 shows the overview of the procedure that involves the initial expansion of melanoma TILs with rhIL-2, which is followed by activation with anti-CD3/CD28 and gene transfer of OCT3/4, KLF4, SOX2, and c-MYC to TILs for the generation of iPSCs. Usually, TILs on culture with rhIL-2 start to form spheres 21-28 days after initiation of culture. At this point, TILs are ready to be activated with anti-CD3/CD28. Figure 2A shows TILs, on culture with rhIL-2 on day 21, that are ready to be activated with anti-CD3/CD28. Figure 2B shows GFP introduction by Sendai virus (SeV) transfected at 20 MOI. Figure 2C shows a typical pluripotent clone on SNL feeder cells that appears 18-21 days after SeV infection. Figure 2D shows that the generated TIL-derived iPSCs have a normal karyotype. Figure 3 shows immunofluorescent staining to confirm pluripotency marker expression on iPSCs (SSEA3, SSEA4, TRA1-81, TRA1-60, and OCT3/4). Figure 4 shows that iPSCs derived from melanoma TILs are able to form teratoma that contain a variety of cells from three germ layers (neural tissue, respiratory epithelium, and cartilage). Figure 5 shows that generated TIL-derived iPSCs retain TCR rearrangements.
Figure 1: Schematic overview of the generation of iPSCs from melanoma TILs. The protocol involves three stages: isolation and culture of TILs with IL-2, T cell activation with anti-CD3/CD28, and cell reprogramming with the Sendai virus (SeV) vector encoding OCT3/4, SOX2, KLF4, and c-MYC. Please click here to view a larger version of this figure.
Figure 2: Generation of iPSCs from melanoma TILs. (A) An image representing the morphology of the TILs in rhIL-2 when they started to expand 2-3 weeks after initiation of the culture. (B) Images representing morphology and GFP expression of TILs one day after SeV infection. (C) A typical ESC-like iPSC colony on day 21 after SeV infection. The Scale bars = 200 µm. (D) Cytogenetic analysis on twenty G-banded metaphase cells from one of the iPSCs derived from melanoma TILs. Figure (D) is adapted from Saito et al16. Please click here to view a larger version of this figure.
Figure 3: Immunofluorescence staining with stem cell pluripotent markers. The immunofluorescence assay shows that the TIL-derived iPSCs from two patients are positive for SSEA3, SSEA4, TRA-1-81, TRA-1-60, and OCT3/4. The Scale bars = 100 µm.The figure is adapted from Saito et al16. Please click here to view a larger version of this figure.
Figure 4: Confirmation of pluripotency for iPSCs with teratoma formation. Hematoxylin- and eosin-stained representative teratoma sections derived from the TIL-derived iPSCs clone (6 weeks post-injection into NOD/SCID mice) are shown. Figure adapted from Saito et al16. Please click here to view a larger version of this figure.
Figure 5: A wide variety of TCR-β gene arrangement patterns in TIL-iPSCs. TCR-β gene rearrangements in TIL-iPSCs are identified by capillary electrophoresis. The green line is derived from the band for the Jβ1 gene, and the blue line is derived from the band for the Jβ2 gene. The figure is adapted from Saito et al16. Please click here to view a larger version of this figure.
Table 1: Composition for the T cell, reprogramming, tumor collecting, SNL feeder cell, and iPSC media, and the permeabilization and blocking buffers. Please click here to view a larger version of this table.
Here, we demonstrated a protocol for reprogramming melanoma TILs to iPSCs by SeV-mediated transduction of the four transcription factors OCT3/4, SOX2, KLF4, and c-MYC. This approach, using a SeV system to reprogram T cells, offers the advantage of a non-integrating method7.
A previous study showed that a SeV reprogramming system was highly efficient and reliable to reprogram not only fibroblasts but also peripheral blood T cells7,17. In addition, we have recently shown that melanoma TILs that are more differentiated and express higher levels of inhibitory receptors such as PD-1 than peripheral blood T cells can also be reprogrammed using SeV vectors16. Timing of stimulation with anti-CD3/CD28 and infection with SeV vector was critical in reprogramming TILs. Peripheral blood T cells can be stimulated with anti-CD3 and IL-2 for reprogramming immediately after harvesting from the subject7, while TILs need to be cultured for 3-4 weeks with IL-2 before stimulation.
Although more than 99% of TILs were CD8 T cells after 3-4 weeks of culture with IL-2 and activation with anti-CD3/CD2816, we recommend analysis of TCR rearrangement in iPSCs to confirm that generated iPSCs are from TILs (Figure 5). Of note, previous studies including ours indicated that every iPSCs generated using SeV from peripheral blood mononuclear cells or TILs had TCR rearrangement7,16.
Although generation of iPSCs from melanoma TILs was feasible, we found that the reprogramming efficiency of melanoma TILs was lower (0.01-0.05 %)16 than that of peripheral blood T cells (0.1%)7. The reason for this remains unclear, but it might be associated with the higher expression of inhibitory receptors or the greater number of differentiated T-cell subsets in TILs13,16. Recent significant progress for reprogramming technology may improve the reprogramming efficiency for generation of TIL-iPSCs. The second generation SeV vector, TS12KOS, was found to have higher efficiency of iPSC generation than the conventional SeV vector used in the previous study18,19.
Although the derivation of human iPSCs with a SeV reprogramming system is feasible, there are several limitations to be considered in this protocol. We use fetal bovine serum during SeV infection in this protocol. We found that the reprogramming efficiency of melanoma TILs was significantly lower if using media with human serum during SeV infection compared to one with fetal bovine serum, despite similar proliferation of TILs. We also use a mouse feeder layer for iPSC generation and maintenance, but a defined feeder-free and xeno-free system may be alternative methods in future studies.
It takes around two months from the time of tumor harvest to generate iPSCs from melanoma TILs. In addition, it would take an additional 1-2 months to obtain transgene-free iPSCs. This might be shortened by the use of the new type of SeV vector, TS12KOS, which has shown a more efficient virus elimination rate19.
In conclusion, the generation of human iPSCs from melanoma TILs is feasible. The current protocol might be an important step for generating an infinite number of tumor-specific T cells for adoptive T cell therapy.
The authors have nothing to disclose.
We thank Ms. Deborah Postiff and Ms. Jackline Barikdar in the Tissue Procurement Core and Dr. Cindy DeLong in the Pluripotent Stem Cell Core Laboratory at the University of Michigan for her technical assistance. This study was supported by University of Michigan startup funding and grants from the Central Surgical Association, American College of Surgeons, Melanoma Research Alliance, and NIH/NCI (1K08CA197966-01) to F. Ito.
gentle MACS C Tubes | Miltenyi Biotec | 130-093-237 | |
gentle MACS Dissociator | Miltenyi Biotec | 130-093-235 | |
Tumor Dissociation Kit, human | Miltenyi Biotec | 130-095-929 | |
RPMI 1640 | Life technologies | 11875-093 | |
Falcon 70 um Cell Strainer | BD | 352350 | |
BD Falcon 50ml Conical Cntrifuge tubes | BD | 352070 | |
IMDM | Life technologies | 12440053 | |
human AB serum | Life technologies | 34005100 | |
L-glutamine (200mM) | Life technologies | 25030-081 | |
2-mercaptoethanol (1000x, 55mM) | Life technologies | 21985-023 | |
Penicillin-Streptomycin | Life technologies | 15140-122 | |
gentamicin | Life technologies | 15750-060 | |
Ficoll-Paque PLUS | GE | 17-1440-02 | |
D-PBS (-) | Life technologies | 14040-133 | |
recombinant human (rh) IL-2 | Aldesleukin, Prometheus Laboratories Inc. | ||
Purified NA/LE Mouse Anti-Human CD3 | BD | 555329 | |
Purified NA/LE Mouse Anti-Human CD28 | BD | 555725 | |
X-VIVO 15 | Lonza | 04-418Q | |
FBS | Gibco | 26140-079 | |
HEPES | Life technologies | 15630-080 | |
N-Acetylcysteine | Cumberland Pharmaceuticals Inc. | NDC 66220-207-30 | |
Falcon Tissue Culture Plates (6-well) | Corning | 353046 | |
Falcon Tissue Culture Plates (24-well) | Corning | 353047 | |
Sendai virus vector | DNAVEC | ||
SNL feeder cells | Cell Biolabs, Inc | CBA-316 | |
mitomycin C | SIGMA | M4287 | soluble in water (0.5 mg/ml) |
gelatin | SIGMA | G1890 | |
Primate ES Cell Medium | Reprocell | RCHEMD001 | warm in 37 ℃ water bath before use |
basic fibroblast growth factor (bFGF) | Life technologies | PHG0264 | |
ReproStem | Reprocell | RCHEMD005 | warm in 37 ℃ water bath before use |