- Email: [email protected]
Vaccinating with Stem Cells to Stop Cancer
TRMOME 1341 No. of Pages 3
Spotlight
Vaccinating with Stem Cells to Stop Cancer Yared Hailemichael,1,3 Manisha Singh,1,3 and Willem Overwijk1,2,* In a recent study, Kooreman and colleagues identify a set of genes expressed in both induced pluripotent stem cells (iPSCs) and cancer cells. Vaccination of mice with iPSCs induces prophylactic and therapeutic anticancer immunity to shared antigens, opening a possible avenue towards rapid generation of iPSC-based, personalized cancer vaccines. Cancer vaccines come in many varieties based on the specific class of antigen (Ag) that is targeted (e.g., normal self-Ags vs neoAgs encoded by mutated genes), the form in which the Ag is delivered (e.g., peptide, protein, DNA/RNA/virus, whole tumor cell), and the formulation of the Ag (e.g., in saline, in mineral oil such as Incomplete Freund’s Adjuvant, in nanoparticles), with or without specific activators of the innate immune system [e.g., CpG, poly I:C, imiquimod, granulocytemacrophage colony-stimulating factor (GM-CSF), viral vector] [1]. Recent promising clinical results point to some of these modalities as potentially therapeutic in patients with cancer [2,3]. Unfortunately, these vaccines thus far show limited success against established bulky disease, and personalized vaccines based on a patient’s unique neoAgs can take months to manufacture. Kooreman and colleagues take a different and potentially transformative approach to anticancer vaccination [4].
cancer cells share patterns of gene expression, since both are rapidly proliferating cells and both need to avoid the immune system (of the mother and of the patient, respectively). Since vaccination with embryonal tissue carries ethical and practical limitations, the investigators focus on iPSCs generated ex vivo from normal skin fibroblasts through transfection with four genes. They found that mouse and human iPSCs share expression of a set of genes with embryonal stem cells and with cancer cells but not with normal tissues, opening the door to using iPSCs as a whole-cell-based cancer vaccine. Four weekly vaccinations with irradiated iPSCs mixed with the immunostimulatory Toll-like receptor 9 (TLR 9) agonist CpG oligodeoxynucleotide induced antibodies that bound to iPSCs but also to tumor cells and, to some extent, normal fibroblasts [4]. Vaccination also induced CD4+ (helper) and CD8+ (cytotoxic) T cells that could recognize tumor cells in vitro, indicating the induction of a systemic antitumor T cell response. Vaccinated mice showed increases in antigen-presenting cells (APCs) and clonally expanded, activated T cells in vivo, resulting in a favorable ratio of cytotoxic (CD8+) T cells over regulatory (CD4+FoxP3+) T cells. Most importantly, vaccinated mice rejected freshly injected melanoma, breast cancer, and mesothelioma tumor cells, indicating that the induced antitumor immunity was functional, while organ histology, antinuclear antibody levels, and animal weight gain were normal, suggesting no gross toxicity or autoimmunity. Transfer of whole splenocytes or purified T cells from immunized mice could transfer this tumor protection to naïve mice, demonstrating that the vaccination-induced T cells mediated the tumor protection [4] (Figure 1).
treat established tumors. Curing rapidly growing tumors with vaccination alone is challenging in patients and even in mice [5] and vaccination with iPSCs did not stop the growth of established melanomas. The authors then modeled a different, clinically relevant scenario of noncurative surgery, in which some tumor remains at the margins. With the need to balance the removal of cancer-invaded normal tissue with sufficient retention of normal tissue structure and function, conventional treatments cannot always render patients completely tumor free, leaving them with a high risk of tumor recurrence. When mice received surgery but were left with microscopic tumors in tumor-draining lymph nodes, vaccination at the resection site, and even CpG injection alone, could reduce tumor recurrence. When a macroscopic tumor mass remained, only the iPSC + CpG vaccine reduced tumor regrowth. The authors should certainly expand on these exciting results in future work, as the animal numbers in these experiments were small and most of the mice were not fully cured. A logical next step would be to repeat these experiments and include concurrent treatment with CTLA-4/PD-1 checkpoint blockade, chemotherapy, or radiotherapy [5]. Another approach would be to increase the magnitude of the induced T cell response by adding immunomodulators that can more potently activate APCs, such as additional TLR agonists, agonistic CD40 monoclonal antibodies (mAbs), or T cell-supportive, engineered cytokines based on IL-2 or IL-15 [1,5]. This could offer powerful combination therapy for large numbers of patients who receive initial standard-ofcare therapy after which they are at high risk for disease recurrence.
Since a scenario in which vaccination preThe team worked on the basis of the cedes the establishment of cancer is clin- A surprising feature of this study is that known observation that embryonal and ically uncommon, the authors also tried to vaccination with iPSCs resulted in lower
Trends in Molecular Medicine, Month Year, Vol. xx, No. yy
1
TRMOME 1341 No. of Pages 3
Normal skin fibroblast + Four genes
iPSC
+ CpGODN + Irradiaon
iPSC vaccine Inject cancer cells
Vaccinaon
Tumor rejecon
Immune response
No vaccinaon
Inject cancer cells Tumor growth
No immune response
Figure 1. Vaccination with Induced Pluripotent Stem Cells (iPSCs) Stops Tumor Growth. Normal skin fibroblasts are transfected with four genes to produce iPSCs, which are irradiated and mixed with CpG oligodeoxynucleotide (ODN) to vaccinate mice and induce iPSC-specific immunity that cross-recognizes cancer cells. Subsequently injected cancer cells are rejected by the vaccination-induced immune response in vaccinated but not in non-vaccinated mice.
blood concentrations of multiple cytokines, including some (IL-6, IL-12, IFNg) known to mediate toxic side-effects in patients receiving immunotherapy with chimeric antigen receptor (CAR) T cells or CTLA-4 or PD-1 checkpoint blockade. Since tumors in the vaccinated animals were presumably much smaller than those in the controls, perhaps this reflects a reduced spontaneous inflammatory response to the reduced tumor mass or possibly even to tumor-derived, antigen-rich exosomes in the circulation; this will be interesting to explore further. 2
The work by Kooreman and colleagues opens an avenue for iPSC-based vaccine therapy for cancer. The approach contrasts with another hotly pursued avenue, which is to produce personalized vaccines with neoAgs encoded by patient-specific mutated gene products. NeoAG-based vaccines have shown promising results in early clinical studies but a drawback is their potentially long manufacturing time and high cost, and thus far modest potency [2,5]. It would be instructive to see a preclinical study that compares manufacturing time, therapeutic efficacy, and estimated cost for vaccination with optimized
Trends in Molecular Medicine, Month Year, Vol. xx, No. yy
vaccines based on personalized neoAgs versus iPSCs. Potentially, iPSCs can be manufactured in bulk, since they may not have to be derived on a per-patient basis. Instead, a universal iPSC-based vaccine could conceivably be created in which expression of the (more or less universal) ‘tumor’ Ags results from the forced induction in iPSCs of the expression of stem-cellassociated genes that are shared between tumors from individual patients. Such an allogeneic off-the-shelf vaccine could be a cost-effective and rapid treatment option for patients with a large variety of cancers. This possibility is easily testable in mice. A much-anticipated experiment would also be to test the vaccine’s potency for prevention of ‘spontaneous’ tumors in mice bearing genetic mutations known to increase cancer risk in humans, such as Braf/PTEN mutations (melanoma), or Kras and p53 (various carcinomas). The present study raises several additional questions. What is the exact Ag specificity of the CD4+ and CD8+ T cells induced by the vaccine? Do they recognize a few or dozens of Ags, possibly reducing the risk of Ag loss by the tumor? Is it also effective to vaccinate with normal fibroblasts? The authors show that iPSCs, but not iPSCs differentiated into endothelial cells, produce an effective vaccine, but this differentiation may have downregulated critical Ags on the endothelial cells that are present on normal fibroblasts and shared with tumors. Do the tumor-binding antibodies facilitate direct tumor cell lysis and/or do they increase tumor Ag presentation through the formation of immune complexes that facilitate Ag uptake by, and activation of, APCs? Are iPSC-based vaccines really not going to cause autoimmunity? It is difficult to imagine that vaccinating with iPSCs and powerful vaccine adjuvants will not also induce at least some degree of immunity to multiple iPSC Ags shared with normal tissues. Mice are notoriously poor predictors of immune-related
TRMOME 1341 No. of Pages 3
adverse events in patients, probably in part due to the comparatively enormous heterogeneity of genetic background, immune/inflammatory status, microbiome, diet and pre-existing diseases in the human population versus the typical laboratory mouse colony [6]. Thus, careful monitoring for autoimmune disease in patients receiving iPSC-based vaccines would be prudent, especially when giving additional immunopotentiating agents. In summary, the work by Kooreman and colleagues opens a new avenue for iPSCbased therapeutic vaccination of patients with cancer. Further preclinical studies
can shed more light on the exact mechanism of action, potency, and utility compared with other modes of anticancer vaccination. It will be interesting to see whether this approach makes it to the clinic and how well it fares. May it become another arrow in the quiver of tomorrow’s oncologist. 1
Department of Melanoma Medical Oncology, University of Texas MD Anderson Cancer Center, Houston, TX, USA
2
MD Anderson Cancer Center UTHealth Graduate School of Biomedical Sciences, Houston, TX, USA 3 These authors contributed equally *Correspondence: [email protected] (W. Overwijk).
References 1. Overwijk, W.W. (2017) Cancer vaccines in the era of checkpoint blockade: the magic is in the adjuvant. Curr. Opin. Immunol. 47, 103–109 2. Ott, P.A. et al. (2017) An immunogenic personal neoantigen vaccine for patients with melanoma. Nature 547, 217–221 3. Zappasodi, R. et al. (2018) Emerging concepts for immune checkpoint blockade-based combination therapies. Cancer Cell 33, 581–598 4. Kooreman, N.G. et al. (2018) Autologous iPSC-based vaccines elicit anti-tumor responses in vivo. Cell Stem Cell 22, 501–513.e7 5. Sahin, U. et al. (2017) Personalized RNA mutanome vaccines mobilize poly-specific therapeutic immunity against cancer. Nature 547, 222–226 6. Masopust, D. et al. (2017) Of mice, dirty mice, and men: using mice to understand human immunology. J. Immunol. 199, 383–388
https://doi.org/10.1016/j.molmed.2018.04.006
Trends in Molecular Medicine, Month Year, Vol. xx, No. yy
3
Spotlight
Vaccinating with Stem Cells to Stop Cancer Yared Hailemichael,1,3 Manisha Singh,1,3 and Willem Overwijk1,2,* In a recent study, Kooreman and colleagues identify a set of genes expressed in both induced pluripotent stem cells (iPSCs) and cancer cells. Vaccination of mice with iPSCs induces prophylactic and therapeutic anticancer immunity to shared antigens, opening a possible avenue towards rapid generation of iPSC-based, personalized cancer vaccines. Cancer vaccines come in many varieties based on the specific class of antigen (Ag) that is targeted (e.g., normal self-Ags vs neoAgs encoded by mutated genes), the form in which the Ag is delivered (e.g., peptide, protein, DNA/RNA/virus, whole tumor cell), and the formulation of the Ag (e.g., in saline, in mineral oil such as Incomplete Freund’s Adjuvant, in nanoparticles), with or without specific activators of the innate immune system [e.g., CpG, poly I:C, imiquimod, granulocytemacrophage colony-stimulating factor (GM-CSF), viral vector] [1]. Recent promising clinical results point to some of these modalities as potentially therapeutic in patients with cancer [2,3]. Unfortunately, these vaccines thus far show limited success against established bulky disease, and personalized vaccines based on a patient’s unique neoAgs can take months to manufacture. Kooreman and colleagues take a different and potentially transformative approach to anticancer vaccination [4].
cancer cells share patterns of gene expression, since both are rapidly proliferating cells and both need to avoid the immune system (of the mother and of the patient, respectively). Since vaccination with embryonal tissue carries ethical and practical limitations, the investigators focus on iPSCs generated ex vivo from normal skin fibroblasts through transfection with four genes. They found that mouse and human iPSCs share expression of a set of genes with embryonal stem cells and with cancer cells but not with normal tissues, opening the door to using iPSCs as a whole-cell-based cancer vaccine. Four weekly vaccinations with irradiated iPSCs mixed with the immunostimulatory Toll-like receptor 9 (TLR 9) agonist CpG oligodeoxynucleotide induced antibodies that bound to iPSCs but also to tumor cells and, to some extent, normal fibroblasts [4]. Vaccination also induced CD4+ (helper) and CD8+ (cytotoxic) T cells that could recognize tumor cells in vitro, indicating the induction of a systemic antitumor T cell response. Vaccinated mice showed increases in antigen-presenting cells (APCs) and clonally expanded, activated T cells in vivo, resulting in a favorable ratio of cytotoxic (CD8+) T cells over regulatory (CD4+FoxP3+) T cells. Most importantly, vaccinated mice rejected freshly injected melanoma, breast cancer, and mesothelioma tumor cells, indicating that the induced antitumor immunity was functional, while organ histology, antinuclear antibody levels, and animal weight gain were normal, suggesting no gross toxicity or autoimmunity. Transfer of whole splenocytes or purified T cells from immunized mice could transfer this tumor protection to naïve mice, demonstrating that the vaccination-induced T cells mediated the tumor protection [4] (Figure 1).
treat established tumors. Curing rapidly growing tumors with vaccination alone is challenging in patients and even in mice [5] and vaccination with iPSCs did not stop the growth of established melanomas. The authors then modeled a different, clinically relevant scenario of noncurative surgery, in which some tumor remains at the margins. With the need to balance the removal of cancer-invaded normal tissue with sufficient retention of normal tissue structure and function, conventional treatments cannot always render patients completely tumor free, leaving them with a high risk of tumor recurrence. When mice received surgery but were left with microscopic tumors in tumor-draining lymph nodes, vaccination at the resection site, and even CpG injection alone, could reduce tumor recurrence. When a macroscopic tumor mass remained, only the iPSC + CpG vaccine reduced tumor regrowth. The authors should certainly expand on these exciting results in future work, as the animal numbers in these experiments were small and most of the mice were not fully cured. A logical next step would be to repeat these experiments and include concurrent treatment with CTLA-4/PD-1 checkpoint blockade, chemotherapy, or radiotherapy [5]. Another approach would be to increase the magnitude of the induced T cell response by adding immunomodulators that can more potently activate APCs, such as additional TLR agonists, agonistic CD40 monoclonal antibodies (mAbs), or T cell-supportive, engineered cytokines based on IL-2 or IL-15 [1,5]. This could offer powerful combination therapy for large numbers of patients who receive initial standard-ofcare therapy after which they are at high risk for disease recurrence.
Since a scenario in which vaccination preThe team worked on the basis of the cedes the establishment of cancer is clin- A surprising feature of this study is that known observation that embryonal and ically uncommon, the authors also tried to vaccination with iPSCs resulted in lower
Trends in Molecular Medicine, Month Year, Vol. xx, No. yy
1
TRMOME 1341 No. of Pages 3
Normal skin fibroblast + Four genes
iPSC
+ CpGODN + Irradiaon
iPSC vaccine Inject cancer cells
Vaccinaon
Tumor rejecon
Immune response
No vaccinaon
Inject cancer cells Tumor growth
No immune response
Figure 1. Vaccination with Induced Pluripotent Stem Cells (iPSCs) Stops Tumor Growth. Normal skin fibroblasts are transfected with four genes to produce iPSCs, which are irradiated and mixed with CpG oligodeoxynucleotide (ODN) to vaccinate mice and induce iPSC-specific immunity that cross-recognizes cancer cells. Subsequently injected cancer cells are rejected by the vaccination-induced immune response in vaccinated but not in non-vaccinated mice.
blood concentrations of multiple cytokines, including some (IL-6, IL-12, IFNg) known to mediate toxic side-effects in patients receiving immunotherapy with chimeric antigen receptor (CAR) T cells or CTLA-4 or PD-1 checkpoint blockade. Since tumors in the vaccinated animals were presumably much smaller than those in the controls, perhaps this reflects a reduced spontaneous inflammatory response to the reduced tumor mass or possibly even to tumor-derived, antigen-rich exosomes in the circulation; this will be interesting to explore further. 2
The work by Kooreman and colleagues opens an avenue for iPSC-based vaccine therapy for cancer. The approach contrasts with another hotly pursued avenue, which is to produce personalized vaccines with neoAgs encoded by patient-specific mutated gene products. NeoAG-based vaccines have shown promising results in early clinical studies but a drawback is their potentially long manufacturing time and high cost, and thus far modest potency [2,5]. It would be instructive to see a preclinical study that compares manufacturing time, therapeutic efficacy, and estimated cost for vaccination with optimized
Trends in Molecular Medicine, Month Year, Vol. xx, No. yy
vaccines based on personalized neoAgs versus iPSCs. Potentially, iPSCs can be manufactured in bulk, since they may not have to be derived on a per-patient basis. Instead, a universal iPSC-based vaccine could conceivably be created in which expression of the (more or less universal) ‘tumor’ Ags results from the forced induction in iPSCs of the expression of stem-cellassociated genes that are shared between tumors from individual patients. Such an allogeneic off-the-shelf vaccine could be a cost-effective and rapid treatment option for patients with a large variety of cancers. This possibility is easily testable in mice. A much-anticipated experiment would also be to test the vaccine’s potency for prevention of ‘spontaneous’ tumors in mice bearing genetic mutations known to increase cancer risk in humans, such as Braf/PTEN mutations (melanoma), or Kras and p53 (various carcinomas). The present study raises several additional questions. What is the exact Ag specificity of the CD4+ and CD8+ T cells induced by the vaccine? Do they recognize a few or dozens of Ags, possibly reducing the risk of Ag loss by the tumor? Is it also effective to vaccinate with normal fibroblasts? The authors show that iPSCs, but not iPSCs differentiated into endothelial cells, produce an effective vaccine, but this differentiation may have downregulated critical Ags on the endothelial cells that are present on normal fibroblasts and shared with tumors. Do the tumor-binding antibodies facilitate direct tumor cell lysis and/or do they increase tumor Ag presentation through the formation of immune complexes that facilitate Ag uptake by, and activation of, APCs? Are iPSC-based vaccines really not going to cause autoimmunity? It is difficult to imagine that vaccinating with iPSCs and powerful vaccine adjuvants will not also induce at least some degree of immunity to multiple iPSC Ags shared with normal tissues. Mice are notoriously poor predictors of immune-related
TRMOME 1341 No. of Pages 3
adverse events in patients, probably in part due to the comparatively enormous heterogeneity of genetic background, immune/inflammatory status, microbiome, diet and pre-existing diseases in the human population versus the typical laboratory mouse colony [6]. Thus, careful monitoring for autoimmune disease in patients receiving iPSC-based vaccines would be prudent, especially when giving additional immunopotentiating agents. In summary, the work by Kooreman and colleagues opens a new avenue for iPSCbased therapeutic vaccination of patients with cancer. Further preclinical studies
can shed more light on the exact mechanism of action, potency, and utility compared with other modes of anticancer vaccination. It will be interesting to see whether this approach makes it to the clinic and how well it fares. May it become another arrow in the quiver of tomorrow’s oncologist. 1
Department of Melanoma Medical Oncology, University of Texas MD Anderson Cancer Center, Houston, TX, USA
2
MD Anderson Cancer Center UTHealth Graduate School of Biomedical Sciences, Houston, TX, USA 3 These authors contributed equally *Correspondence: [email protected] (W. Overwijk).
References 1. Overwijk, W.W. (2017) Cancer vaccines in the era of checkpoint blockade: the magic is in the adjuvant. Curr. Opin. Immunol. 47, 103–109 2. Ott, P.A. et al. (2017) An immunogenic personal neoantigen vaccine for patients with melanoma. Nature 547, 217–221 3. Zappasodi, R. et al. (2018) Emerging concepts for immune checkpoint blockade-based combination therapies. Cancer Cell 33, 581–598 4. Kooreman, N.G. et al. (2018) Autologous iPSC-based vaccines elicit anti-tumor responses in vivo. Cell Stem Cell 22, 501–513.e7 5. Sahin, U. et al. (2017) Personalized RNA mutanome vaccines mobilize poly-specific therapeutic immunity against cancer. Nature 547, 222–226 6. Masopust, D. et al. (2017) Of mice, dirty mice, and men: using mice to understand human immunology. J. Immunol. 199, 383–388
https://doi.org/10.1016/j.molmed.2018.04.006
Trends in Molecular Medicine, Month Year, Vol. xx, No. yy
3