DLTs=occurrence of any of following adverse events (AEs) attributable to PF-07263689 in first cycle (cycle=28 days): Hematologic: grade(G)4 neutropenia lasting >5 days; febrile neutropenia; G3 neutropenia with infection, thrombocytopenia with bleeding; G4 thrombocytopenia. Non-hematologic: any treatment-related G>=3 toxicity; clinical events consistent with Hy's law; any G3 cytokine release syndrome (CRS) not improving to G<=2 within 72 hours despite medical management; any G4 CRC; G>=3 toxicity of any duration affecting vital organs; G4 vaccinia infection lasting >=6 days; G>=3 toxicities persisting for >3 days despite medical therapy (e.g. nausea, vomiting, diarrhea, fatigue); G >=3 rash not resolving to G<2 within 21 days with supportive measures; G>=3 lab abnormalities not controlled to G <=2 with or without appropriate medical management within 3 days; treatment-related AE inducing a delay by 2 weeks in receiving next scheduled dose; clinically important or persistent toxicities.

DLT evaluable set included participants who received 3 of the 4 doses of PF-07263689 and had completed the scheduled safety assessments during the DLT observation period or had experienced a DLT. Data is not reported for Part 1b as no participants were enrolled and data was not collected.

An AE was any untoward medical occurrence in a participant, temporally associated with the use of study treatment, whether or not considered related to the study treatment. An SAE was defined as any untoward medical occurrence that at any dose met 1 or more of the following criteria: resulted in death, was life-threatening; resulted in persistent or significant disability/incapacity; was a congenital anomaly/birth defect; a suspected transmission via a Pfizer product of an infectious agent, pathogenic or non-pathogenic; an important medical event; required inpatient hospitalization or prolongation of existing hospitalization. TEAE was defined as any adverse event that occurred during the on-treatment period, on or after the first dose of study treatment. Relatedness was based on investigator's assessment.

Safety analysis set included all enrolled participants who received at least one dose of study treatment. Data is not reported for Part 1b as no participants were enrolled and data was not collected.

An AE was any untoward medical occurrence in a participant, temporally associated with the use of study treatment, whether or not considered related to the study treatment. TEAE was defined as any AE that occurred during the on-treatment period, on or after the first dose of study treatment. AEs were graded using CTCAE version 5 where, grade 1=mild AE; grade 2=moderate AE; grade 3=severe AE; grade 4= life-threatening; urgent intervention indicated; and grade 5= death related to AE.

Safety analysis set included all enrolled participants who received at least one dose of study treatment. Data is not reported for Part 1b as no participants were enrolled and data was not collected.

Hematology abnormalities were graded using CTCAE version 5 where, grade 0=non-missing lab value outside the grading range for the corresponding lab parameter; grade 1=mild; grade 2=moderate; grade 3=severe; grade 4= life-threatening. Only those categories with non-zero values for any of the arms have been reported.

Safety analysis set included all enrolled participants who received at least one dose of study treatment. Data is not reported for Part 1b as no participants were enrolled and data was not collected.

Clinical chemistry abnormalities were graded using CTCAE version 5 where, grade 0=non-missing lab value outside the grading range for the corresponding lab parameter; grade 1=mild; grade 2=moderate; grade 3=severe; grade 4= life-threatening. Only those categories with non-zero values for any of the arms have been reported.

Safety analysis set included all enrolled participants who received at least one dose of study treatment. Data is not reported for Part 1b as no participants were enrolled and data was not collected. Here, 'Number Analyzed' signifies participants evaluable for the specified rows.

An AE was any untoward medical occurrence in a participant, temporally associated with the use of study treatment, whether or not considered related to the study treatment. An SAE was defined as any untoward medical occurrence that at any dose met 1 or more of the following criteria: resulted in death, was life-threatening; resulted in persistent or significant disability/incapacity; was a congenital anomaly/birth defect; a suspected transmission via a Pfizer product of an infectious agent, pathogenic or non-pathogenic; an important medical event; required inpatient hospitalization or prolongation of existing hospitalization. TEAE was defined as any adverse event that occurred during the on-treatment period, on or after the first dose of study treatment. Relatedness was planned to be assessed by investigator.

Data was not collected as no participants were enrolled in Part 2 of the study due to study termination.

AEs were planned to be graded using CTCAE version 5 where, grade 1=mild AE; grade 2=moderate AE; grade 3=severe AE; grade 4= life-threatening; urgent intervention indicated; and grade 5= death related to AE.

Data was not collected as no participants were enrolled in Part 2 of the study due to study termination.

Hematology and clinical chemistry parameters were planned to be assessed.

Data was not collected as no participants were enrolled in Part 2 of the study due to study termination.

ORR was defined as the percentage of participants with a best overall response of complete response (CR) or partial response (PR) and was determined using Response Evaluation Criteria In Solid Tumors (RECIST) version 1.1. CR: disappearance of all target and non-target lesions and normalization of tumor marker level, all lymph nodes must be non-pathological in size (<10 millimeter [mm] short axis), PR: at least 30 percent (%) decrease in sum of diameters of target lesions, taking as reference the baseline sum diameters. Short diameter was used in the sum for target nodes, while the longest diameter was used in the sum for all other target lesions.

Data was not collected as no participants were enrolled in Part 2 of the study due to study termination.

ORR was defined as the percentage of participants with a best overall response of CR or PR and was determined using RECIST version 1.1. CR: disappearance of all target and non-target lesions and normalization of tumor marker level, all lymph nodes must be non-pathological in size (<10 mm short axis), PR: at least 30% decrease in sum of diameters of target lesions, taking as reference the baseline sum diameters. Short diameter was used in the sum for target nodes, while the longest diameter was used in the sum for all other target lesions. 95% confidence interval (CI) was based on Clopper-Pearson method.

Response evaluable set included all participants who received at least one dose of study treatment and had baseline disease assessment [or measurable disease at baseline, if applicable] and at least one post-baseline disease assessment. Data is not reported for Part 1b as no participants were enrolled and data was not collected.

Duration of response was defined as the time from first documentation of CR or PR to date of first documentation of progressive disease (PD) or death due to any cause. CR: disappearance of all target and non-target lesions and normalization of tumor marker level, all lymph nodes must be non- pathological in size (<10 mm short axis), PR: at least 30% decrease in sum of diameters of target lesions, taking as reference the baseline sum diameters. Short diameter was used in the sum for target nodes, while the longest diameter was used in the sum for all other target lesions. PD: 20% increase in the sum of diameters of target measurable lesions above the smallest sum observed (over baseline if no decrease in the sum was observed during therapy), with a minimum absolute increase of 5 mm and unequivocal progression of pre-existing lesions.

Response evaluable set included all participants who received at least one dose of study treatment and had baseline disease assessment [or measurable disease at baseline, if applicable] and at least one post-baseline disease assessment. Only participants with CR or PR were analyzed. Data is not reported for Part 1b as no participants were enrolled and data was not collected.

Progression free survival was defined as time from start date of treatment to the date of first documentation of PD or death due to any cause. PD was defined as 20% increase in the sum of diameters of target measurable lesions above the smallest sum observed (over baseline if no decrease in the sum was observed during therapy), with a minimum absolute increase of 5 mm and unequivocal progression of pre-existing lesions. 95% CI was based on Brookmeyer and Crowley method.

Full analysis set included all enrolled participants. Data is not reported for Part 1b as no participants were enrolled and data was not collected.

Time to progression was defined as the time from start date of treatment to the date of the first documentation of PD. PD was defined as 20% increase in the sum of diameters of target measurable lesions above the smallest sum observed (over baseline if no decrease in the sum was observed during therapy), with a minimum absolute increase of 5 mm and unequivocal progression of pre-existing lesions. 95% CI was based on Brookmeyer and Crowley method.

Full analysis set included all enrolled participants. Data is not reported for Part 1b as no participants were enrolled and data was not collected.

Blood viral load Kinetics Analysis Set included all enrolled participants treated who did not have protocol deviations influencing viral load kinetics assessment, and had sufficient information to estimate at least 1 of the parameters of interest. Data is not reported for Part 1b as no participants were enrolled and data was not collected.

Blood viral load Kinetics Analysis Set included all enrolled participants treated who did not have protocol deviations influencing viral load kinetics assessment, and had sufficient information to estimate at least 1 of the parameters of interest. Data is not reported for Part 1b as no participants were enrolled and data was not collected.

Blood viral load Kinetics Analysis Set included all enrolled participants treated who did not have protocol deviations influencing viral load kinetics assessment, and had sufficient information to estimate at least 1 of the parameters of interest. Data is not reported for Part 1b as no participants were enrolled and data was not collected.

Data was not collected as no participants were enrolled in Part 1b of the study due to study termination.

Viral titers in each matrix (saliva, urine and skin swabs [30 days post last dose only]) at 30, 45 and 60 days after last dose of study treatment is reported in this outcome measure.

Vector Shedding Analysis Set included all enrolled participants who were treated and had at least 1 analyte concentration above the lower limit of quantitation. Data is not reported for Part 1b as no participants were enrolled and data was not collected. Here, 'Overall Number of Participants Analyzed' signifies participants evaluable for this outcome measure and contributed data to the table and 'Number Analyzed' signifies participants evaluable for the specified time points.

A participant was considered NAb positive if (1) baseline titer was missing or negative and participant had >= 1 post-treatment positive titer (treatment-induced) or (2) positive titer at baseline and had a ratio of >= 4 in titer (dilution) to baseline in >= 1 post-treatment sample (treatment-boosted). Percentage of participants with positive neutralizing antibodies against PF-07263689 is presented in this outcome measure. Data was not collected for sasanlimab as no participants were enrolled in Part 1b of the study.

Immunogenicity analysis set included all enrolled participants who received at least one dose of study treatment and had at least one sample tested for ADA. Data is not reported for Part 1b as no participants were enrolled and data was not collected.

A participant was considered anti-drug antibody (ADA) positive if (1) baseline titer was missing or negative and participant had >= 1 post-treatment positive titer (treatment-induced) or (2) positive titer at baseline and had a ratio of >= 4 in titer (dilution) to baseline in >= 1 post-treatment sample (treatment-boosted). Percentage of participants with positive anti-interleukin 2 antibodies against PF-07263689 is presented in this outcome measure.

Immunogenicity analysis set included all enrolled participants who received at least one dose of study treatment and had at least one sample tested for ADA. Data is not reported for Part 1b as no participants were enrolled and data was not collected.

Data was not collected as no participants were enrolled in Part 2 of the study due to study termination.

Data was not collected as no participants were enrolled in Part 2 of the study due to study termination.

Data was not collected as no participants were enrolled in Part 2 of the study due to study termination.

Data was not collected as no participants were enrolled in Part 2 of the study due to study termination.

Data was not collected as no participants were enrolled in Part 2 of the study due to study termination.

Data was not collected as no participants were enrolled in Part 2 of the study due to study termination.

Data was not collected as no participants were enrolled in Part 2 of the study due to study termination.

Data was not collected as no participants were enrolled in Part 2 of the study due to study termination.

Data was not collected as no participants were enrolled in Part 2 of the study due to study termination.

Disease control rate was the percentage of participants with CR, PR or stable disease (SD), as defined by RECIST 1.1. CR: disappearance of all target and non-target lesions and normalization of tumor marker level, all lymph nodes must be non-pathological in size (<10 mm short axis), PR: at least 30% decrease in sum of diameters of target lesions, taking as reference the baseline sum diameters. Short diameter was used in the sum for target nodes, while the longest diameter was used in the sum for all other target lesions. SD: Does not qualify for CR, PR, or progression. All target lesions assessed.

Data was not collected as no participants were enrolled in Part 2 of the study due to study termination.

Duration of response was defined as the time from first documentation of CR or PR to date of first documentation of progressive disease (PD) or death due to any cause. CR: disappearance of all target and non-target lesions and normalization of tumor marker level, all lymph nodes must be non- pathological in size (<10 mm short axis), PR: at least 30% decrease in sum of diameters of target lesions, taking as reference the baseline sum diameters. Short diameter was used in the sum for target nodes, while the longest diameter was used in the sum for all other target lesions. PD: 20% increase in the sum of diameters of target measurable lesions above the smallest sum observed (over baseline if no decrease in the sum was observed during therapy), with a minimum absolute increase of 5 mm and unequivocal progression of pre-existing lesions.

Data was not collected as no participants were enrolled in Part 2 of the study due to study termination.

Progression free survival was defined as time from start date of treatment to the date of first documentation of PD or death due to any cause. PD was defined as 20% increase in the sum of diameters of target measurable lesions above the smallest sum observed (over baseline if no decrease in the sum was observed during therapy), with a minimum absolute increase of 5 mm and unequivocal progression of pre-existing lesions.

Data was not collected as no participants were enrolled in Part 2 of the study due to study termination.

Time to progression was defined as the time from start date of treatment to the date of the first documentation of PD. PD was defined as 20% increase in the sum of diameters of target measurable lesions above the smallest sum observed (over baseline if no decrease in the sum was observed during therapy), with a minimum absolute increase of 5 mm and unequivocal progression of pre-existing lesions.

Data was not collected as no participants were enrolled in Part 2 of the study due to study termination.

Overall survival was defined as the duration from the start of study treatment to the date of death from any cause.

Data was not collected as no participants were enrolled in Part 2 of the study due to study termination.