Inclusion Criteria
* Participants must have histologically confirmed advanced melanoma and have been selected for, eligible for, and consented for treatment with standard-of-care TIL (Iovance).
* Participants must have two additional metastases that are measurable based on RECIST 1.1 criteria, one of which must have low surgical morbidity, defined as dermal, subcutaneous, soft tissue, or nodal metastasis not requiring entry into the abdominal or pelvic cavity to harvest.
* Age ≥18 years. Because no dosing or adverse event data are currently available on the use of crefmirlimab in Participants \<18 years of age, children are excluded from this study.
* The effects of crefmirlimab on the developing human fetus are unknown. For this reason and because standard-of-care TIL used in this trial are known to be teratogenic, women of child-bearing potential and men must agree to use adequate contraception (hormonal or barrier method of birth control; abstinence) prior to study entry and for the duration of study participation. (Refer to Pregnancy Assessment Policy MD Anderson Institutional Policy # CLN1114). This includes all female Participants, between the onset of menses (as early as 8 years of age) and 55 years unless the Participant presents with an applicable exclusionary factor which may be one of the following:
* Postmenopausal (no menses in greater than or equal to 12 consecutive months).
* History of hysterectomy or bilateral salpingo-oophorectomy.
* Ovarian failure (Follicle Stimulating Hormone and Estradiol in menopausal range, who have received Whole Pelvic Radiation Therapy).
* History of bilateral tubal ligation or another surgical sterilization procedure.
* Approved methods of birth control are as follows: Hormonal contraception (i.e. birth control pills, injection, implant, transdermal patch, vaginal ring), Intrauterine device (IUD), Tubal Ligation or hysterectomy, Subject/Partner post vasectomy, Implantable or injectable contraceptives, and condoms plus spermicide. Not engaging in sexual activity for the total duration of the trial and the drug washout period is an acceptable practice; however periodic abstinence, the rhythm method, and the withdrawal method are not acceptable methods of birth control. Should a woman become pregnant or suspect she is pregnant while she or her partner is participating in this study, she should inform her treating physician immediately.
* Men treated or enrolled on this protocol must also agree to use adequate contraception prior to the study, for the duration of study participation, and 4 months after completion of \[Agent\] administration.
* Ability to understand and the willingness to sign a written informed consent document.
Exclusion Criteria
* Participants who are not eligible and consented for standard-of-care Iovance TIL therapy.
* Participants who are due to receive standard-of-care Iovance TIL therapy in less than 28 days.
* Participants who are receiving any other investigational agents.
* Participants with psychiatric illness/social situations that would limit compliance with study requirements.
* Pregnant women are excluded from this study because crefmirlimab is radioactive substance with the potential for teratogenic or abortifacient effects. Because there is an unknown but potential risk for adverse events in nursing infants' secondary to treatment of the mother with crefmirlimab, breastfeeding should be discontinued if the mother is treated with crefmirlimab. These potential risks may also apply to other agents used in this study.
