A Study of XmAb®22841 Monotherapy & in Combination w/ Pembrolizumab in Subjects w/ Selected Advanced Solid Tumors

Inclusion Criteria:

1. All subjects' cancer must have progressed after treatment with all available therapies
that are known to confer clinical benefit, or are intolerant to treatment, or refuse
standard treatment.

2. All subjects must have adequate archival tumor.

3. Subjects have an ECOG performance status of 0-1.

4. Subjects in monotherapy and combination therapy cohorts must have histologically or
cytologically confirmed advanced or metastatic solid tumors, including the following:

1. Melanoma (excluding uveal melanoma)

2. Cervical carcinoma

3. Pancreatic carcinoma

4. Breast carcinoma that is estrogen receptor, progesterone receptor, and Her2
negative (TNBC)

5. Hepatocellular carcinoma

6. Urothelial carcinoma

7. Squamous cell carcinoma of the head and neck (HNSCC)

8. Nasopharyngeal carcinoma (NPC)

9. Renal cell carcinoma

10. Colorectal or endometrial carcinoma

11. Small cell lung carcinoma or NSCLC

12. Gastric or gastroesophageal junction adenocarcinoma

13. Subjects in the combination cohorts in Part A with XmAb22841 and pembrolizumab
must have histologically or cytologically confirmed advanced solid tumors for
which pembrolizumab is an approved indication and that has not previously been
treated with an agent targeting PD1 or PDL1.

Exclusion Criteria:

1. Prior treatment with an investigational anti-LAG3 therapy.

2. Treatment with any CTLA4 antibody within 18 weeks of the start of study drug (7 weeks
for XmAb22841 cohorts ≥ 4).

3. Systemic antineoplastic therapy, unconjugated antibody therapy within 4 weeks of the
first dose of study treatment; or radiotherapy within 2 weeks of the first dose of
study treatment; or small molecule kinase inhibitors within 6 elimination half-lives
of the first dose of study treatment.

4. Have received prior therapy with an anti-PD1, anti-PDL1, or anti PDL2 agent or with an
agent directed to another stimulatory or co-inhibitory T-cell receptor (eg, CTLA4, OX
40, CD137) AND were discontinued from that treatment due to a Grade 3 or higher IRAE.

5. Failure to recover from any IRAE from prior cancer therapy to Grade ≤ 1.

6. Failure to recover from any other toxicity (other than immune-related toxicity)
related to previous anticancer treatment to Grade ≤ 2.

7. Active known or suspected autoimmune disease (except that subjects are permitted to
enroll if they have vitiligo; type 1 diabetes mellitus; residual hypothyroidism due to
an autoimmune condition that is treatable with hormone replacement therapy only;
psoriasis, atopic dermatitis, or another autoimmune skin condition that is managed
without systemic therapy; or arthritis that is managed without systemic therapy beyond
oral acetaminophen and non-steroidal anti-inflammatory drugs).

8. Receipt of an organ allograft.

9. Treatment with antibiotics within 14 days prior to first dose of study drug.