MRx0518 and Pembrolizumab Combination Study

Inclusion Criteria:

- Willing and able to provide written informed consent/assent for the trial.

- ≥18 years of age on day of signing informed consent.

- Histological or cytological evidence of advanced and/or metastatic or recurrent NSCLC,
renal cell carcinoma, bladder cancer or melanoma.

- At least one measurable lesion per RECIST v 1.1 criteria.

- Failure to respond or intolerance to standard therapy or for whom no appropriate
therapies are known to provide clinical benefit (per the judgement of the
Investigator).

- Subjects must have progressed on treatment with a PD-1 inhibitor administered either
as monotherapy, or in combination with other checkpoint inhibitors or other therapies.
PD-1 inhibitor treatment progression is defined by meeting all of the following
criteria:

1. Has received at least 2 doses of a PD-1 inhibitor.

2. Has demonstrated disease progression after PD-1 therapy as defined by RECIST
v1.1, iRECIST or irRECIST. The initial evidence of disease progression (PD) is to
be confirmed by a second assessment no less than four weeks from the date of the
first documented PD, in the absence of rapid clinical progression.

3. Progressive disease has been documented within 12 weeks from the last dose of a
PD-1 inhibitor.

- Have adequate organ function

- Be willing to provide archival tissue

- Eastern Cooperative Oncology Group (ECOG) performance status of 0 or 1.

- Female subjects of childbearing potential should have a negative serum pregnancy test
within 72 hours prior to receiving the first dose of study medication. Subjects of
childbearing potential are those who have not been surgically sterilized or have not
been free from menses for ≥2 years.

- Female subjects of childbearing potential should be willing to use 2 methods of birth
control or be surgically sterile, or abstain from heterosexual activity for the course
of the study through 120 days after the last dose of study medication

- Male subjects with female partners of childbearing potential should agree to use an
adequate method of contraception starting with the first dose of study therapy through
120 days after the last dose of study therapy.

Exclusion Criteria:

- Subjects who failed to show any response to initial treatment with PD-1 inhibitor
(i.e. no Response or no Stable Disease).

- Has active brain metastases or leptomeningeal disease. Subjects with asymptomatic CNS
metastases which have been stable (defined as without evidence of progression by MRI
for at least 28 days prior to initiation of therapy and any neurologic symptoms have
returned to baseline) following treatment with surgery or radiation therapy are
allowed.

- Prior solid organ or hematologic transplant.

- Treatment-related immune-mediated (or immune related) AEs from immune-modulatory
agents (including but not limited to anti-PD1/PD-L1 agents, anti-CTLA4 monoclonal
antibodies) that caused permanent discontinuation of the agent, or that were grade 3
or 4 in severity.

- Subjects treated with chemotherapy, immunotherapy, biologic therapy, or other
investigational agent within <5 times the half-life of the agent or <21 days
(whichever is shorter) of starting study drug. Continuation of hormone replacement
therapy is permitted. Stable regimens of hormonal therapy i.e. for prostate cancer
(e.g. leuprolide, a GnRH agonist), ovarian, or breast cancer are not exclusionary.

- Subjects treated with tyrosine kinase inhibitor therapy or completed palliative
radiotherapy <14 days from initiation of therapy.

- Comorbidity requiring corticosteroid therapy (>10mg prednisone/day or equivalent)
within 7 days of starting experimental therapy. Physiologic replacement doses are
allowed if they are ≤10mg of prednisone/day or equivalent, as long as they are not
being administered for immunosuppressive intent. Inhaled or topical steroids are
permitted, provided that they are not for treatment of an autoimmune disorder.

- Significant cardiac dysfunction