## 2 Results
### Tumor Clearance Induced by Opsonization and CD47 Deletion Prolongs Survival, but Some Tumors Escape
not significant, ordinary one-way ANOVA, \(n=5\) per group except isotype control \(n=4\)). Right: Tumor burden in a separate experiment comparing control (untreated) or 2\(\times\) A\({}^{\prime}\)PB groups. Lung tumor burden was assessed on day 14 post-inoculation. Mean and s.e.m. (* \(p<\) 0.05; this data is part of the experiment in Figure 7B, which describes the statistical test). (**C**) Projected survival advantages in A\({}^{\prime}\)PB-treated lung tumors. (n = 10 for control group, n = 5 per treatment group, **** < 0.0001, Log-rank test). (**D**) Variance of tumor areas scales with average tumor area of lung nodules, consistent with power law growth. Mathematically, any given cohort within an experiment shows higher variation for larger mean tumor size (Figure 5D), which is expected for any set of exponential-type growth curves that start with small engraftment differences (e.g., Figure 2 Biii). Moreover, the mouse-to-mouse variation (s.e.m.) in the sizes of lung metastases scales with mean for a cohort, with similar findings for subcutaneous tumors. Greater variation with lung metastases seems consistent nonetheless with post-intravenous engraftment of multiple nodules (Figure 2 Bi). These trends in variance allow us to use our exponential-type fits of day 14 data (Figure 2B) and calculate both the mean size and s.e.m. for days 16 and 20, with our best estimates showing WT versus (WT + anti-Tyrp1) do not differ significantly. Such modeling can thus minimize unnecessary animal testing, particularly given the very good agreement in measured versus projected survival (Figure 4A,B). Overall, our results for WT CD47 metastases agree with the CD47 deletion results and suggest a promising therapeutic strategy to suppress tough-to-treat metastases. WT Human Lung Cancer Metastases in Liver Suppressed by Antibody-Engineered Marrow Macrophages/Monocytes  
To assess the A'PB antibody-engineered marrow macrophages/monocytes in a second metastatic model and to assess relevance to humans, liver metastases of human lung cancer A549 tumors were first established in immunocompromised NSG mice (Figure 6A,B), as previously described by our group [31]. A549 expression of tdTomato enables imaging of infiltrative nodules after engraftment in liver via surgical implantation (Figure 6 Bi,ii). Macrophages in NSG mice express a SIRP\(\alpha\) variant that favors engraftment of human cells due to its high affinity with human CD47, but NSG mice lack antibodies and functional T cells, B cells, and NK cells [32; 33]. Compared to B16F10 tumors that show exponential phase growth from 100 to 200 mm [2] in 2-3 days (Figure 2 Biv), A549 tumors grow more slowly with linear growth to the same extent in \(\sim\)2 weeks (Figure 6 Biii). A'PB treatment of these liver metastatic A549 tumors combined with a tumor-opsonizing antibody regimen (polyclonal anti-human IgG) led to exponential tumor shrinkage of \(\sim\)50% within days, consistent with our model for growth vs. phagocytic clearance (Figure 6 Bii). Regression is transient, but aligns with our previous results for A549 subcutaneous tumors that had shown (i) that an opsonizing antibody alone has no significant effect and that (ii) injected macrophages show progressively less evidence of phagocytosis over time as they differentiate toward a tumor-associated macrophage phenotype [29]. These results further illustrate that for slow-growing solid tumors, macrophage phagocytosis can be engineered or otherwise controlled to dominate tumor growth, in agreement with the proposed mathematical model (Figure 3 Bii). B16F10 melanoma tumors grow so rapidly that phagocytosis can only slow the tumor doubling time, but human melanomas grow slowly at rates of \(<\)1 mm per month [34]. A549 tumors grow significantly faster at \(>\)10 mm per month. Hence, antibody-engineered marrow macrophages/monocytes in marrow with SIRP\(\alpha\)-blockade and clinically relevant anti-Tyrp1 [23] can in principle out-compete and thereby repress human metastatic melanoma.