The ErbB network is dysregulated in many solid tumors. To exploit this, we have 
developed a chimeric Ag receptor (CAR) named T1E28z that targets several 
pathogenetically relevant ErbB dimers. T1E28z is coexpressed with a chimeric 
cytokine receptor named 4αβ (combination termed T4), enabling the selective 
expansion of engineered T cells using IL-4. Human T4(+) T cells exhibit 
antitumor activity against several ErbB(+) cancer types. However, ErbB receptors 
are also expressed in several healthy tissues, raising concerns about toxic 
potential. In this study, we have evaluated safety of T4 immunotherapy in vivo 
using a SCID beige mouse model. We show that the human T1E28z CAR efficiently 
recognizes mouse ErbB(+) cells, rendering this species suitable to evaluate 
preclinical toxicity. Administration of T4(+) T cells using the i.v. or 
intratumoral routes achieves partial tumor regression without clinical or 
histopathologic toxicity. In contrast, when delivered i.p., tumor reduction is 
accompanied by dose-dependent side effects. Toxicity mediated by T4(+) T cells 
results from target recognition in both tumor and healthy tissues, leading to 
release of both human (IL-2/IFN-γ) and murine (IL-6) cytokines. In extreme 
cases, outcome is lethal. Both toxicity and IL-6 release can be ameliorated by 
prior macrophage depletion, consistent with clinical data that implicate IL-6 in 
this pathogenic event. These data demonstrate that CAR-induced cytokine release 
syndrome can be modeled in mice that express target Ag in an appropriate 
distribution. Furthermore, our findings argue that ErbB-retargeted T cells can 
achieve therapeutic benefit in the absence of unacceptable toxicity, providing 
that route of administration and dose are carefully optimized.