**2. Intratumoral delivery of pathogen-associated molecules**

Probably the most famous historical account on the use of pathogens to treat tumors is that of William Coley. He was the first to report the observation that soft tissue sarcoma could naturally regress after bacterial infections. Facing cases in his clinical practice, he then proceeded to cause such risky infections on purpose, using bacterial-derived material (Coley's toxins) to locally inject tumor masses, observing successful tumor regression in some case [26–28].

Another well-known example of an infectious pathogen used for local tumor treatment is that of Calmette-Guerrin bacillus for transurethral instillation in urothelial carcinoma [29].

We are today able to deliver much better defined preparations of engineered recombinant viruses and bacteria into tumors, as well as of a variety of pathogenderived molecules to trigger the immune response. In general, the presence of pathogens is sensed by specialized immune cell receptors [30].

Main families of these receptors are: toll-like receptors (TLRs) on the plasma membrane and in endosomal compartments, cytoplasmic receptors for viral nucleic acids, such as retinoic acid-induced gene 1 (RIG-I), melanoma differentiationassociated protein 5 (MDA-5), stimulator of interferon genes (STING), and the intracellular nucleotide-binding oligomerization domain-like receptors (NOD) family of receptors. They are also entangled and shared by those that detect stressful cell death (DAMPs) secondary to infectious conditions. Therefore, many types of PAMP and DAMP agonists are under study alone and/or in combination with other immune system activators, such as CIs but also immune cell direct activators and growth stimulators.

Pharmaceutical formulations of polyinosinic: polycytosinic acids (poly I:C) can mimic double-stranded RNA molecules of viral origin sensed by the endosomal TLR3 receptors and by the intracellular RIG-I and MDA-5 sensors, and have been studied in transplantable mouse tumors, yielding good results in combination with checkpoint inhibitors [31]. Stabilized poly I:C formulation (poly ICLC, Hiltonol) has been employed for intratumoral delivery as monotherapy and/or in combination, in a few clinical trials [31–33].

TLR7/8 natural agonists imiquimod and resiquimod have been used against basal cell carcinoma [34, 35], melanoma, and other skin neoplasms [36] as well as against common warts [37, 38]. Local imiquimod has also been used in combination with radiotherapy for breast cancer in the clinic [39]. Intratumoral administration of TLR7/8 agonist NKTR-262 is being studied in patients with locally advanced or metastatic solid tumors (NCT03435640). Preliminary results from the phase I/II REVEAL trial noted a disease control rate of about 50% [40].

Intratumoral delivery of TLR9 agonists CpG oligonucleotides has been employed very successfully in mouse models and seen to be able to even determine cancer eradication by the immune system [41]; but, it failed to provide clear benefits in clinical trials [42, 43]. A combination of a CpG oligonucleotide with an agonistic anti-OX40 antibody intratumorally administered both in syngeneic transplanted and genetically determined tumor models was able to induce complete tumor eradication in mice [44] and the combination of these two agents (namely SD-101 and BMS 986178) is now under testing in ongoing trial against a variety of tumors (NCT03831295).

Intratumoral injection of STING-agonist dinucleotides can be another way to unleash the curative tumor response against transplantable mouse models [45]. Human STING agonist adu-s100, for instance, is undergoing clinical development (NCT 02675439).

**165**

*Repurposing Infectious Pathogen Vaccines in Cancer Immunotherapy*

All these immune activators should be delivered intratumorally, ideally in a neoadjuvant setting, in order to synergize with current systemic immunotherapies (**Figure 3**).

*Schematic diagram of the neoadjuvant intratumoral delivery of a therapeutic vaccine.*

Entire pathogens, in particular recombinant oncolytic viruses, have been engineered to sustain selective replication into malignant cells [46, 47]. However, experience with the use of these oncolytic viruses, originally thought as cytolytic agents, has shown that antitumor immune response against viral-infected cells is a fundamental factor for their anticancer efficacy [48]. Therefore, modern viral vectors are genetically engineered to also express cytokines and other immune

Vaccinia and herpes viruses have proven most effective when engineered to encode for immune-promoting genes such as interleukin 12 (IL-12) and granulocyte macrophage colony-stimulating factor (GM-CSF) [49, 50]. These agents are dramatically enhanced in their therapeutic performances by concomitant administration of PD-1/PDL-1 and CTLA-4 blocking Abs [51] as well as anti-CD137 or anti-OX40 agonist Abs [52–54]. Vectors based on vaccinia virus encoding GM-CSF (JX-594) are also under clinical development with promising results [55, 56].

The most successful agent so far in this category is herpes virus (HSV-1) modi-

fied to encode GM-CSF, named T-vec (talimogene). It has been granted Food and Drug Administration approval for unresectable melanoma [57]. Essentially, engineered pathogen preparations are delivered intratumorally in the neoadjuvant

Immunotherapies do not come without adverse effects and complications. In addition, patients have their own peculiarities and it is vital that clinicians identify the best therapeutic options for each one of them. In this light, there are various ongoing clinical trials evaluating intratumoral immunotherapies based on pathogen-associated molecules, alone or in combination with other therapies [25]. Poly-ICLC (Hiltonol) is in phase I against prostate cancer (NCT03262103); TLR7 agonist (Imiquimod) is in phase III against melanoma (NCT01720407);

**4. Clinical trials on intratumorally delivered pathogens and** 

setting (essentially according to the scheme in **Figure 3**).

**pathogen-associated molecules**

*DOI: http://dx.doi.org/10.5772/intechopen.92780*

**3. Intratumoral delivery of pathogens**

stimulating factors [49].

**Figure 3.**

*Repurposing Infectious Pathogen Vaccines in Cancer Immunotherapy DOI: http://dx.doi.org/10.5772/intechopen.92780*

**Figure 3.**

*Drug Repurposing - Hypothesis, Molecular Aspects and Therapeutic Applications*

**2. Intratumoral delivery of pathogen-associated molecules**

successful tumor regression in some case [26–28].

pathogens is sensed by specialized immune cell receptors [30].

urothelial carcinoma [29].

and growth stimulators.

tion, in a few clinical trials [31–33].

Probably the most famous historical account on the use of pathogens to treat tumors is that of William Coley. He was the first to report the observation that soft tissue sarcoma could naturally regress after bacterial infections. Facing cases in his clinical practice, he then proceeded to cause such risky infections on purpose, using bacterial-derived material (Coley's toxins) to locally inject tumor masses, observing

Another well-known example of an infectious pathogen used for local tumor treatment is that of Calmette-Guerrin bacillus for transurethral instillation in

We are today able to deliver much better defined preparations of engineered recombinant viruses and bacteria into tumors, as well as of a variety of pathogenderived molecules to trigger the immune response. In general, the presence of

Main families of these receptors are: toll-like receptors (TLRs) on the plasma membrane and in endosomal compartments, cytoplasmic receptors for viral nucleic acids, such as retinoic acid-induced gene 1 (RIG-I), melanoma differentiationassociated protein 5 (MDA-5), stimulator of interferon genes (STING), and the intracellular nucleotide-binding oligomerization domain-like receptors (NOD) family of receptors. They are also entangled and shared by those that detect stressful cell death (DAMPs) secondary to infectious conditions. Therefore, many types of PAMP and DAMP agonists are under study alone and/or in combination with other immune system activators, such as CIs but also immune cell direct activators

Pharmaceutical formulations of polyinosinic: polycytosinic acids (poly I:C) can mimic double-stranded RNA molecules of viral origin sensed by the endosomal TLR3 receptors and by the intracellular RIG-I and MDA-5 sensors, and have been studied in transplantable mouse tumors, yielding good results in combination with checkpoint inhibitors [31]. Stabilized poly I:C formulation (poly ICLC, Hiltonol) has been employed for intratumoral delivery as monotherapy and/or in combina-

TLR7/8 natural agonists imiquimod and resiquimod have been used against basal cell carcinoma [34, 35], melanoma, and other skin neoplasms [36] as well as against common warts [37, 38]. Local imiquimod has also been used in combination with radiotherapy for breast cancer in the clinic [39]. Intratumoral administration of TLR7/8 agonist NKTR-262 is being studied in patients with locally advanced or metastatic solid tumors (NCT03435640). Preliminary results from the phase I/II

Intratumoral delivery of TLR9 agonists CpG oligonucleotides has been employed

very successfully in mouse models and seen to be able to even determine cancer eradication by the immune system [41]; but, it failed to provide clear benefits in clinical trials [42, 43]. A combination of a CpG oligonucleotide with an agonistic anti-OX40 antibody intratumorally administered both in syngeneic transplanted and genetically determined tumor models was able to induce complete tumor eradication in mice [44] and the combination of these two agents (namely SD-101 and BMS 986178) is now under testing in ongoing trial against a variety of tumors

Intratumoral injection of STING-agonist dinucleotides can be another way to unleash the curative tumor response against transplantable mouse models [45]. Human STING agonist adu-s100, for instance, is undergoing clinical development

REVEAL trial noted a disease control rate of about 50% [40].

**164**

(NCT03831295).

(NCT 02675439).

*Schematic diagram of the neoadjuvant intratumoral delivery of a therapeutic vaccine.*

All these immune activators should be delivered intratumorally, ideally in a neoadjuvant setting, in order to synergize with current systemic immunotherapies (**Figure 3**).
