With sequencing as a standard frontline protocol to identify emerging viruses such 25 zika virus and SARS-CoV2, direct utilization of sequence data to program antivirals 26 against the viruses could accelerate drug development to treat their infections. 27 CRISPR-Cas effectors are promising candidates that could be programmed to 28 inactivate viral genetic material based on sequence data but several challenges such 29 as delivery and design of effective crRNA need to be addressed to realize practical 30 use. Here, we showed that virus-like particle (VLP) could deliver PspCas13b-crRNA To characterize the antiviral activity of CRISPR-Cas13 against flavivirus, we first 61 established a stable BHK21 clone (BHK21-Cas13b) that could be induced with 62 doxycycline to express PspCas13b using lentivirus (Supplementary Figure 1a) . 63
Type I-interferon defective BHK21 cell line was chosen as the host cell for its ability 64 to support high level of dengue virus (DENV) and zika virus (ZIKV) replication (Liu et 65 al., 2006) , providing a robust platform to evaluate viral suppression activity. 66
Inducible expression system appeared to provide the stability of Cas13b cassette in 67 BHK21 as we were not able to maintain PspCas13b expression under a constitutive for subsequent experiments (Supplementary Figure 1b) . Though Figure 1b) . The suppression of DENV2-mCherry by mCh3 crRNA 80 was specific as other reporter DENV2 could not be suppressed by the crRNA in both 81 single-virus infection and co-infection settings (Supplementary Figures 1c-d) . 82
Using BHK21-Cas13b, we individually tested 51 crRNAs against the targets on 83 DENV2 reporter viruses, DENV2-16681 (NS5 gene), and ZIKV-SV0010 (NS2A 84 gene) (Supplementary Table 1 (Pewkliang et al., 2018) ). The 118
VLP was effective at delivering YFP to these cells (Supplementary Figure 1b) . We 119 found that the VSV-G pseudotyped VLP preferentially target CD14 + monocytes in 120 (Supplementary Figures 3a-b) . Nevertheless, the 142 knock-down activity of two crRNAs (mAmet1 and 8681) were aggravated by 22-nt 143 spacer (Supplementary Figures 3a-b) . We selected three pairs of 30-nt vs. 22-nt crRNAs for testing by VLP delivery in BHK21 cells. The knock-down enhancement 145 was recapitulated with Cas13b RNP delivery by VLP for 22-nt vs. 30-nt mCh3 146 crRNAs (Figure 3c) . In contrast to the results in BHK21-Cas13b, the 22-nt mAmet-1 147 crRNA could knock down DENV2-mAmet with much less PspCas13b than its 30-nt 148 counterpart (Figure 3c) . The dose-response curves indicated that the 22-nt mCh3 149 and mAmet1 crRNAs needed 15-20 folds less of PspCas13b than 30-nt crRNAs to 150 achieve the same level of virus suppression (Figure 2c) The isolated CD14 + monocytes were cultured in R10 supplemented with 5% HI-316 human AB serum to allow differentiation into macrophages (Brugger et al., 1991) . crRNA array with three crRNAs, 2x = crRNA array with two crRNAs, 1x = singlet